test GHA cache in the PR

Author: leofang

.github/workflows/build-and-test.yml

@@ -93,6 +93,9 @@ jobs:
             echo "USE_CACHE=0" >> $GITHUB_ENV
           fi
 
+          # TODO: revert me before merging; this is to test the cache restore in the PR
+          echo "USE_CACHE=1" >> $GITHUB_ENV
+
       - name: Dump environment
         run: |
           env