Allow overwrite option to be modified for pull mirroring without deleting/re-adding

Summary

When force-pushing to a remote branch (in this case the master branch) on a repository that is mirrored by GitLab (pull mirror) the update fails:

The default branch (master) has diverged from its upstream counterpart and could not be updated automatically.

Steps to reproduce

• Setup a new repository in GitLab and enable pull mirroring from another (remote) repository
• Wait until the initial pull has completed
• Force push to the master branch in the remote repository
• Either wait or force mirror update
• Observe e.g. "Failed to update 11 minutes ago. Last successful update 2 months ago. " on the repository's project tab
• Observe "The default branch (master) has diverged from its upstream counterpart and could not be updated automatically." on the /mirror page

Expected behavior

A mirror should always be in sync with its (authoritative) source

Actual behavior

GitLab fails to keep the mirror in sync

Relevant logs and/or screenshots

Example repository:

https://gitlab.com/HearthSim/HSReplay.net

https://gitlab.com/HearthSim/HSReplay.net/mirror

Output of checks

n/a (occuring on gitlab.com)

Results of GitLab application Check

n/a (occuring on gitlab.com)

Results of GitLab environment info

n/a (occuring on gitlab.com)

Possible fixes

• Always overwrite mirrors with changes from the remote repository
• Add a checkbox whether to overwrite the mirror with changes from the remote repository
• Add a button to do a one-time forced overwrite on the /mirror page