fix: skip token revocation when no token was acquired (#918)

Add a check for non-empty github_token output before attempting to
revoke the app token in the cleanup step. When the prepare phase fails
(e.g., unsupported event type with track_progress), no token is
acquired, causing the cleanup curl to send an empty Bearer token
and produce a confusing "Bad credentials" 401 error.

Fixes #858

Co-authored-by: Dave-London <hello@os4us.org>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

action.yml

@@ -335,7 +335,7 @@ runs:
         bun run ${GITHUB_ACTION_PATH}/src/entrypoints/post-buffered-inline-comments.ts
 
     - name: Revoke app token
-      if: always() && inputs.github_token == '' && steps.run.outputs.skipped_due_to_workflow_validation_mismatch != 'true'
+      if: always() && inputs.github_token == '' && steps.run.outputs.github_token != '' && steps.run.outputs.skipped_due_to_workflow_validation_mismatch != 'true'
       shell: bash
       run: |
         curl -L \