fix: add a specific error message for the commit queue (#645)

Author: aduh95

lib/landing_session.js

@@ -406,8 +406,13 @@ export default class LandingSession extends Session {
 
       if (!forceLand) {
         cli.info(
-          'Use --fixupAll option, squash the PR manually or land the PR from ' +
-          'the command line.'
+          'GITHUB_ACTION' in process.env
+
+            ? 'Add `commit-queue-squash` label to land the PR as one commit, ' +
+            'or `commit-queue-rebase` to land as separate commits.'
+
+            : 'Use --fixupAll option, squash the PR manually or land the PR ' +
+            'from the command line.'
         );
         process.exit(1);
       }