[Netatalk-admins] Sonar branch scanning restored

[Daniel M. <mar...@gm...>]

After much tinkering (sorry for the PR noise!) I got Sonar scanning working
again on branches.
Scanning PRs always worked, but ever since I tried to disable fork PR
scanning, branch scanning hasn't been working.

I also updated the Sonar settings to use 'main' as the main development
branch (not 'master').

Now code quality feedback should be fully functional again:
https://sonarcloud.io/summary/new_code?id=Netatalk_netatalk