Switch over to Codecov v5

[A5rocks]

This is a debug PR, I don't want to clutter up https://github.com/python-trio/trio/pull/3161

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 100.00000%. Comparing base (8571ef2) to head (a31d536). :warning: Report is 90 commits behind head on main.

Additional details and impacted files

@@               Coverage Diff               @@
##                 main        #3285   +/-   ##
===============================================
  Coverage   100.00000%   100.00000%           
===============================================
  Files             127          125    -2     
  Lines           19266        19250   -16     
  Branches         1301         1301           
===============================================
- Hits            19266        19250   -16     

see 2 files with indirect coverage changes

:rocket: New features to boost your workflow:

• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[A5rocks]

Spotted:

• It seems to be using the wrong path for Alpine (it includes the full path including the .venv)
• It seems to be ignoring our specified coverage ignore lines

[A5rocks]

First part is fixed

[A5rocks]

OK nevermind that fixes both issues, @webknjaz in case you want to copy these changes to your PR.

[A5rocks]

Turns out I can't modify that PR to add in a few commits. I guess codecov v5 isn't that urgent anyways though.