Fix sccache for forked PRs (#28)

* Add sccache debug logging

* Use read-only default instead of explicit specifying it

* Try read-write acces

* Clean up for submission

sccache/action.yml

@@ -56,13 +56,13 @@ runs:
       shell: bash
       run: |
         echo "SCCACHE_GCS_KEY_PATH=${{ steps.auth.outputs.credentials-file }}" >> $GITHUB_ENV
-        echo "SCCACHE_GCS_RW_MODE=READ_ONLY" >> $GITHUB_ENV
         echo "SCCACHE_GCS_BUCKET=protobuf-sccache" >> $GITHUB_ENV
         echo "SCCACHE_GCS_KEY_PREFIX=${{ inputs.cache-prefix }}" >> $GITHUB_ENV
 
     # Only trusted runs should have write access to our caches.
-    - name: Disable sccache cache writing
-      if: ${{ github.event_name != 'pull_request_target' }}
+    - name: Enable sccache cache writing
+      # Always use read-write mode because of https://github.com/mozilla/sccache/issues/1886
+      #if: ${{ github.event_name != 'pull_request_target' }}
       shell: bash
       run: echo "SCCACHE_GCS_RW_MODE=READ_WRITE" >> $GITHUB_ENV