Update ci.yaml

Author: tinder-maxwellelliott

.github/workflows/ci.yaml

@@ -25,4 +25,4 @@ jobs:
         run: go get github.com/bazelbuild/bazelisk
       - uses: actions/checkout@v2
       - name: Run bazel-diff tests
-        run: USE_BAZEL_VERSION=last_rc ~/go/bin/bazelisk test //test/...
+        run: USE_BAZEL_VERSION=last_downstream_green ~/go/bin/bazelisk test //test/...