ci: enhance coverage data handling in GitHub Actions workflow

- Updated the coverage data upload step to include the Python version in the artifact name.
- Modified the download step to use a pattern for coverage data and enabled merging of multiple artifacts.

Author: ekalinin

.github/workflows/main.yml

@@ -43,9 +43,10 @@ jobs:
         TOXENV=$(tox --listenvs | grep "^py$ENV_PREFIX" | tr '\n' ',') tox
 
     - name: Upload coverage data
+      if: always()
       uses: actions/upload-artifact@v6
       with:
-        name: coverage-data
+        name: coverage-data-${{ matrix.python-version }}
         path: '.coverage.*'
 
   coverage:
@@ -65,7 +66,8 @@ jobs:
       - name: Download data
         uses: actions/download-artifact@v7
         with:
-          name: coverage-data
+          pattern: coverage-data-*
+          merge-multiple: true
 
       - name: Combine coverage and fail if it's <100%
         run: |