fix: make sure mentions of local users get rendered correctly during AP delivery

What does this PR do? (Please give us a brief description of what this PR does.) This PR makes sure that mentions of local users get rendered correctly during AP delivery.

Contribution Guidelines By submitting this merge request, you agree to follow our Contribution Guidelines

• I agree to follow this project's Contribution Guidelines
• I have made sure to test this pull request

Resolves: #645 (closed)

added bugbackend label

approved this merge request

approved this merge request

merged

mentioned in commit c59852f8

added federation label