Update GitHub Actions upload/download artifacts to v4

The GitHub Actions workflow artifacts for uploading coverage data and documentation have been updated to v4. The coverage data now includes the Python matrix parameter in its name. Its download has been adjusted accordingly, now supports multiple entries merge and matches pattern 'coverage-data-*'.

Author: tasansal

.github/workflows/tests.yml

@@ -97,14 +97,14 @@ jobs:
 
       - name: Upload coverage data
         if: always() && matrix.session == 'tests'
-        uses: "actions/upload-artifact@v3"
+        uses: actions/upload-artifact@v4
         with:
-          name: coverage-data
+          name: coverage-data-${{ matrix.python }}
           path: ".coverage.*"
 
       - name: Upload documentation
         if: matrix.session == 'docs-build'
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: docs
           path: docs/_build
@@ -138,9 +138,10 @@ jobs:
           nox --version
 
       - name: Download coverage data
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
-          name: coverage-data
+          pattern: coverage-data-*
+          merge-multiple: true
 
       - name: Combine coverage data and display human readable report
         run: |