always upload cache

.github/workflows/run-tests.yml

@@ -75,7 +75,8 @@ jobs:
             build-ccache-master
 
       - name: Prepare build cache for branch/tag
-        uses: actions/cache@v2
+        # use a fork of actions/cache@v2 to upload cache even when the build or test failed
+        uses: pat-s/always-upload-cache@v2.1.0
         if: github.event_name != 'pull_request'
         with:
           path: /home/runner/QGIS/.ccache