Improve error for PRs from forks (#159)

This has confused us a few times.

.github/ci/common.sh

@@ -8,14 +8,7 @@ set -o xtrace    # print command traces before executing command
 
 # Wraps the common Bazel flags for CI for brevity.
 function bazel_ci {
-  BAZELRC="${DIR}/rbe.bazelrc"
-  # GitHub does not give non-org members access to repo secrets.
-  # If that is the case, fall back to a non-RBE (ie slow) build.
-  if ! jq -e . >/dev/null 2>&1 < robco_integration_test_credentials.json; then
-      echo "Failed to parse RBE credentials, this is expected iff this is a PR from an external contributor/bot" >&2
-      BAZELRC="/dev/null"
-  fi
-  bazel --bazelrc="${BAZELRC}" "$@"
+  bazel --bazelrc="${DIR}/.bazelrc" "$@"
 }
 
 function generate_build_id() {

.github/workflows/check-bazel.yml

@@ -22,11 +22,18 @@ jobs:
         env:
           ROBCO_INTEGRATION_TEST_GITHUB_ROBOT_JSON_KEY: ${{ secrets.ROBCO_INTEGRATION_TEST_GITHUB_ROBOT_JSON_KEY }}
         run: |
+          if [[ -z "$ROBCO_INTEGRATION_TEST_GITHUB_ROBOT_JSON_KEY" ]] ; then
+            echo >&2 "This PR appears to be from a fork or authored by a non-org member, rather than from the primary repo."
+            echo >&2 "This means it can't run the presubmit, which requires access to GCR."
+            echo >&2 "If you are a project member, please push your branch to github.com/googlecloudrobotics/core instead."
+            echo >&2 "https://docs.github.com/en/actions/managing-workflow-runs/approving-workflow-runs-from-public-forks#about-workflow-runs-from-public-forks"
+            exit 1
+          fi
           echo "$ROBCO_INTEGRATION_TEST_GITHUB_ROBOT_JSON_KEY" > robco_integration_test_credentials.json
       - name: Run .github/ci/presubmit.sh
         env:
           USE_BAZEL_VERSION: "6.2.0"
         run: ./.github/ci/presubmit.sh
       - name: Get bazel server logs
         if: success() || failure()
-        run: cat ~/.cache/bazel/_bazel_*/*/java.log
+        run: cat ~/.cache/bazel/_bazel_*/*/java.log || true