Sometimes when merging a pull request, the activity says that the merge succeeded, but it actually didn't:

Steps to reproduce:

1. Create a plugin that merges pull requests simultaneously on multiple threads
2. Create a pull request
3. Merge with the plugin

Expected: One thread will succeed in merging the pull requests, the others will fail. The activity for the thread that succeeded will display on the pull request and the pull request will be in a merged state.

Actual: The pull request remains open. There is a merge activity on the pull request

Cause:
The locking in the merge pull request method is not working as expected