Migrate to v4 of upload/download artifact

Author: Preocts

.github/workflows/python-tests.yml

@@ -52,7 +52,7 @@ jobs:
       - name: "Save coverage artifact"
         uses: "actions/upload-artifact@5d5d22a31266ced268874388b861e4b58bb5c2f3"
         with:
-          name: "coverage-artifact"
+          name: "coverage-artifact-${{ matrix.os}}-${{ matrix.python-version}}"
           path: ".coverage.*"
           retention-days: 1
 
@@ -76,7 +76,9 @@ jobs:
       - name: "Download coverage artifacts"
         uses: "actions/download-artifact@c850b930e6ba138125429b7e5c93fc707a7f8427"
         with:
-          name: coverage-artifact
+          name: "coverage-artifacts"
+          pattern: "coverage-artifact-*"
+          merge-multiple: true
 
       - name: "Compile coverage data, print report"
         run: |