fix: run pytest directly from venv for lowest-direct tests

The issue was that 'uv run' (even with --no-sync) was still interacting
with the project configuration and potentially re-resolving packages.

Solution: For lowest-direct tests, bypass uv run entirely and execute
pytest directly from the venv: .venv/bin/pytest

This ensures we use exactly what was installed by --resolution lowest-direct
without any interference from uv's project management or lockfile validation.

For highest tests, continue using 'uv run --frozen --no-sync pytest' which
validates against the lockfile as intended.

Github-Issue: #1325

Author: felixweinberger

.github/workflows/shared.yml

@@ -77,7 +77,13 @@ jobs:
           uv run --frozen --no-sync python -c "from importlib.metadata import version; print('anyio version:', version('anyio'))" || echo "Failed with --frozen"
 
       - name: Run pytest
-        run: uv run ${{ matrix.dep-resolution.name == 'lowest-direct' && '--no-sync' || '--frozen --no-sync' }} pytest
+        shell: bash
+        run: |
+          if [ "${{ matrix.dep-resolution.name }}" == "lowest-direct" ]; then
+            .venv/bin/pytest
+          else
+            uv run --frozen --no-sync pytest
+          fi
 
   readme-snippets:
     runs-on: ubuntu-latest