test: Move codecov.yml to root directory

[philipphofmann]

Move the codecov.yml so Codecov uses it. The current yml that Codecov uses is bogus:

codecov:
  branch: main
  notify:
    wait_for_ci: true
  require_ci_to_pass: true
comment:
  after_n_builds: 5
  behavior: default
  layout: reach,diff,flags,files,footer
  require_changes: false
coverage:
  range:
  - 85.0
  - 100.0
ignore:
- ^Tests/SentryTests.*
parsers:
  gcov:
    branch_detection:
      conditional: true
      loop: true
      macro: false
      method: false

Furthermore, remove some default values.

#skip-changelog

[codecov]

Codecov Report

Merging #2991 (d84cb1b) into main (3a01b17) will decrease coverage by 0.311%.
The diff coverage is n/a.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #2991       +/-   ##
=============================================
- Coverage   80.538%   80.227%   -0.311%     
=============================================
  Files          265       265               
  Lines        24695     24686        -9     
  Branches     10947     10930       -17     
=============================================
- Hits         19889     19805       -84     
- Misses        4191      4322      +131     
+ Partials       615       559       -56     

see 43 files with indirect coverage changes

---

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[philipphofmann]

#2991 (comment) is not correct. This should be fixed once we merge the yml to main.