[CI] MlMappingsUpgradeIT testMappingsUpgrade failing

[mark-vieira]

This looks to be broken on the 7.16 when testing against version 7.8 - 7.13.

Build scan:
https://gradle-enterprise.elastic.co/s/zu3r5bmq3kqey/tests/:x-pack:qa:rolling-upgrade:v7.13.3%23upgradedClusterTest/org.elasticsearch.upgrades.MlMappingsUpgradeIT/testMappingsUpgrade

Reproduction line:
./gradlew ':x-pack:qa:rolling-upgrade:v7.13.3#upgradedClusterTest' -Dtests.class="org.elasticsearch.upgrades.MlMappingsUpgradeIT" -Dtests.method="testMappingsUpgrade" -Dtests.seed=EE393E50638716F8 -Dtests.bwc=true -Dtests.locale=bg -Dtests.timezone=Libya -Druntime.java=8

Applicable branches:
7.16

Reproduces locally?:
Didn't try

Failure history:
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.upgrades.MlMappingsUpgradeIT&tests.test=testMappingsUpgrade

Failure excerpt:

java.lang.AssertionError: 
Expected: an empty collection
     but: <[.ml-notifications-000002]>

  at __randomizedtesting.SeedInfo.seed([EE393E50638716F8:C342DA07EA186D9C]:0)
  at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
  at org.junit.Assert.assertThat(Assert.java:956)
  at org.junit.Assert.assertThat(Assert.java:923)
  at org.elasticsearch.upgrades.MlMappingsUpgradeIT.lambda$assertMlLegacyTemplatesDeleted$2(MlMappingsUpgradeIT.java:190)
  at org.elasticsearch.test.ESTestCase.assertBusy(ESTestCase.java:1123)
  at org.elasticsearch.test.ESTestCase.assertBusy(ESTestCase.java:1096)
  at org.elasticsearch.upgrades.MlMappingsUpgradeIT.assertMlLegacyTemplatesDeleted(MlMappingsUpgradeIT.java:182)
  at org.elasticsearch.upgrades.MlMappingsUpgradeIT.testMappingsUpgrade(MlMappingsUpgradeIT.java:69)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java:-2)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:498)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.invoke(RandomizedRunner.java:1750)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$8.evaluate(RandomizedRunner.java:938)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$9.evaluate(RandomizedRunner.java:974)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$10.evaluate(RandomizedRunner.java:988)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.util.TestRuleSetupTeardownChained$1.evaluate(TestRuleSetupTeardownChained.java:49)
  at org.apache.lucene.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:45)
  at org.apache.lucene.util.TestRuleThreadAndTestName$1.evaluate(TestRuleThreadAndTestName.java:48)
  at org.apache.lucene.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:64)
  at org.apache.lucene.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:47)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:368)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.forkTimeoutingTask(ThreadLeakControl.java:817)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$3.evaluate(ThreadLeakControl.java:468)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.runSingleTest(RandomizedRunner.java:947)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$5.evaluate(RandomizedRunner.java:832)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$6.evaluate(RandomizedRunner.java:883)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$7.evaluate(RandomizedRunner.java:894)
  at org.apache.lucene.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:45)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.util.TestRuleStoreClassName$1.evaluate(TestRuleStoreClassName.java:41)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.util.TestRuleAssertionsRequired$1.evaluate(TestRuleAssertionsRequired.java:53)
  at org.apache.lucene.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:47)
  at org.apache.lucene.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:64)
  at org.apache.lucene.util.TestRuleIgnoreTestSuites$1.evaluate(TestRuleIgnoreTestSuites.java:54)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:368)
  at java.lang.Thread.run(Thread.java:748)

[elasticmachine]

Pinging @elastic/ml-core (Team:ML)

[droberts195]

Since this is causing so much build noise and the fix was a one-liner I just pushed it directly:

master: 873553a
8.0: 8b40c3a
7.16: 9d77b0b

Logically this fix is part of #80876/#80874 so doesn't need separately release-noting.