Also save cache if build failed.

We only cache dependencies (which should not fail to build).
Caching partial or failed build allows for faster iteration while fixing
the workflow file as the llvm build will not always restart from scratch.

.github/workflows/build_and_test.yml

@@ -32,6 +32,13 @@ jobs:
 
       - name: Build 
         run: .github/workflows/build-ci.sh
+      - uses: actions/cache/save@v3
+        if: always()
+        with:
+          path: |
+            - llvm
+            - upmem
+          key: cinnamon-dependencies-${{ runner.os }}
 
       - name: Test
         working-directory: cinnamon/build