bump CI action upload-artifact to v4

Author: Sispheor

.github/workflows/on-pull-request-workflow.yml

@@ -54,7 +54,7 @@ jobs:
           poetry run coverage lcov
 
       - name: 'Upload Artifact'
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: htmlcov
           path: htmlcov