ci(phpunit): don't run in server master

[hamza221]

context : https://github.com/nextcloud/contacts/actions/runs/15514540343/job/43679743708
#4475

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 11.02%. Comparing base (f69b5e1) to head (9a79231).
Report is 2 commits behind head on stable7.1.

Additional details and impacted files

@@               Coverage Diff               @@
##             stable7.1    #4497      +/-   ##
===============================================
+ Coverage         2.30%   11.02%   +8.72%     
- Complexity           0      265     +265     
===============================================
  Files               96      122      +26     
  Lines             4823     5594     +771     
  Branches          1212     1212              
===============================================
+ Hits               111      617     +506     
- Misses            4590     4855     +265     
  Partials           122      122              

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