Fix broken Mergify url from mergify.io to mergify.com

[koju]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.80%. Comparing base (f0dfaa6) to head (430e7bb).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3604   +/-   ##
=======================================
  Coverage   89.80%   89.80%           
=======================================
  Files         174      174           
  Lines        5031     5031           
  Branches      493      493           
=======================================
  Hits         4518     4518           
  Misses        513      513           

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[fthomas]

Thanks!