Don't run repository sync on branch deletion.

[johannesbulin]

Fixed an issue with the sync action that propagates changes from Github to Bitbucket. The problem was that

• only pushes to the main branch were propagated to Bitbucket.
• deleting any branch in Github also triggered a corresponding branch-delete in Bitbucket.

So when a non-main branch was created in Github, it was not replicated in Bitbucket (only the main branch). When such a branch was deleted in Github, the sync action tried to delete it in Bitbucket as well, where it didn't exist, causing an error.

I've fixed this by disabling the delete trigger in the sync.yml action. As we only want to keep main in sync (and won't delete this branch at any point), the delete sync isn't necessary.

The alternative would be to sync all branches to Bitbucket, even short-lived branches for pull-requests.

[mlange05]

Yes, looks good to me.