ci: Windows CI does not collect coverage, breaks Codecov patch check for Windows-only code

[mr-raj12]

Problem

The Windows CI job in .github/workflows/ci.yml (line 662) runs pytest without --cov:

  python -m pytest -n4 --benchmark-skip -vv -rs -k "not remote" --junitxml=test-results.xml

The Linux/macOS jobs use tox, which includes --cov=borg --cov-config=pyproject.toml, so coverage is generated and uploaded to Codecov. The Windows job skips coverage entirely, even though pytest-cov is already installed via scripts/msys2-install-deps.

This means any PR adding Windows-only source code (e.g., platform/windows.pyx) will always fail the codecov/patch check with 0% coverage, regardless of test quality. PR #9389 is currently affected with all CI checks green, tests passing, but Codecov reports "0.00% of diff hit (target 76.47%)".

CI job	Test runner	Coverage collected?
Linux/macOS (native_tests)	tox with --cov=borg	Yes
Windows (windows_tests)	pytest directly	No

Proposed fix

Add --cov=borg --cov-config=pyproject.toml to the Windows pytest command, matching what tox uses for Linux/macOS:

# before
python -m pytest -n4 --benchmark-skip -vv -rs -k "not remote" --junitxml=test-results.xml

# after
python -m pytest -n4 --benchmark-skip -vv -rs -k "not remote" --cov=borg --cov-config=pyproject.toml --junitxml=test-results.xml

• pytest-cov is already available — scripts/msys2-install-deps installs mingw-w64-ucrt-x86_64-python-pytest-cov
• The coverage config in pyproject.toml ([tool.coverage.run]) is platform-agnostic and works as-is
• One-line change in .github/workflows/ci.yml