[SAC] Gitea upgraded to 1.5.1+

I've upgraded Gitea to 1.5, we were coming from 1.3.
What the upgrade brings us is:

- Autocompletion of mentions
- Reactions (like, smiles etc)
- .patch and .diff for pull requests (Regina: this may fix Jenkins
- Pull Request merge options (rebase, squash etc.)
- Multiple assignees for issues

Plus a ton of other improvements/fixes

Please report any issue that arises from this upgrade.