Fix codecov configuration to properly enforce coverage thresholds

[Copilot]

The codecov configuration was causing CI failures even when coverage changes were within the configured 2% threshold. This affected PRs like #5315 where project coverage moved by less than 2% but CI still failed.

Problem

The issue had two root causes:

1. Incorrect codecov.yml configuration: The patch.threshold: 2% setting allowed patch coverage to drop by 2%, but the requirement is that patches should maintain at least 80% coverage
2. GitHub workflow override: The fail_ci_if_error: true setting in codecov-action was causing premature CI failures, potentially overriding codecov's own threshold logic

Solution

Fixed codecov.yml configuration

coverage:
  status:
    project:
      default:
        target: auto
        threshold: 2%          # Allow project coverage to drop up to 2%
    patch:
      default:
        target: 80%           # Require 80% minimum coverage for patches
        # Removed threshold to prevent coverage drops
ignore:
  - "**/*.md"
  - "docs/**/*"             # Ignore documentation files

Updated GitHub workflow

Changed fail_ci_if_error: false in the codecov-action to rely on codecov.yml thresholds instead of failing on upload errors that might mask legitimate threshold-based passes.

Expected Behavior

After this fix:

• Project coverage drops ≤ 2%: ✅ Pass (addresses the original issue)
• Project coverage drops > 2%: ❌ Fail
• Patch coverage ≥ 80%: ✅ Pass
• Patch coverage < 80%: ❌ Fail
• Changes only to .md files: ✅ Ignored

This ensures that codecov properly handles the randomized test behavior mentioned in the issue while still enforcing the required coverage standards.

Fixes #5322.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.40%. Comparing base (4aeadf8) to head (428f1e9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5323      +/-   ##
==========================================
- Coverage   86.58%   86.40%   -0.19%     
==========================================
  Files          59       59              
  Lines       18331    18331              
==========================================
- Hits        15872    15838      -34     
- Misses       2459     2493      +34     

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[guhetier]

Note to reviewer: we may have to monitor / confirm this is behaving as we want on PR with more churn.
The behavior without this PR causes some spurious failures and this should improve it, but it is hard to fully validate.