Switch from archived matrix-org/gomatrix to mautrix/go

[Johennes]

This switches from https://github.com/matrix-org/gomatrix (which is archived) to https://github.com/mautrix/go.

Pull Request Checklist

• Pull request includes a sign off

[codecov]

Codecov Report

❌ Patch coverage is 53.84615% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.91%. Comparing base (c9c4687) to head (8029bac).

Files with missing lines	Patch %	Lines
fclient/federationclient.go	25.00%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #466   +/-   ##
=======================================
  Coverage   53.90%   53.91%           
=======================================
  Files          52       52           
  Lines        6025     6026    +1     
=======================================
+ Hits         3248     3249    +1     
  Misses       2363     2363           
  Partials      414      414           

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[Johennes]

Looks like this won't be as straightforward as I thought because apparently dendrite would require changes, too.