Merge button does not refresh when PR is approved

Summary

Similar regression on ---BSERV-3190--- except this is only triggered only after when a user wants to add themselves as a reviewer of a PR. If a user gets invited to a PR instead, this bug doesn't get affected (the 'Merge' button will be enabled or disabled appropriately). 

Steps to Reproduce

1. Create a second user and provide write access to a repository
2. Create a Pull Request and set the minimum number for approval to 1
3. Login as the second user and add as a reviewer of the Pull Request
4. Approve that PR

Expected Results

The Merge button is enabled and a comment saying that the second user had approve the PR

Actual Results

The Merge button is still disabled and nothing is written on the comment

Workaround

Refresh the PR page. After refreshing, the merge button should work as expected if the conditions are met.