WIP: github: Try to add restore-keys

Author: mstorsjo

.github/workflows/build.yml

@@ -411,8 +411,10 @@ jobs:
         with:
           path: /opt/cache
           key: tarballs-${{ hashFiles('build-make.sh') }}
+          restore-keys: |
+            tarballs
       - name: Restore cache
-        if: steps.cache-tarballs.outputs.cache-hit
+        if: steps.cache-tarballs.outputs.cache-hit != ''
         run: |
           ln -s /opt/cache/*.tar.* .
       - name: Build