Remove phpdbg from coverage target

[ohmyfelix]

Summary

Replace the coverage Makefile target to run Tester with php instead of phpdbg.

Motivation

This aligns the skeleton with the org-wide migration tracked in contributte/contributte#73 and keeps new coverage runs compatible with the shared CI PHP setup.

Changes

• switch Makefile coverage target from -p phpdbg to -p php

Testing

• Tests pass locally
• CI passes
• Manual verification

Manual verification:

• make coverage now invokes vendor/bin/tester -s -p php ...
• local coverage execution is blocked in this environment because PHP lacks Xdebug/PCOV (phpdbg is no longer used)
• CI uses contributte/.github/.github/actions/setup-php, whose default coverage input is xdebug

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 23.20%. Comparing base (b9919b8) to head (c76b85e).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #544      +/-   ##
==========================================
+ Coverage   18.84%   23.20%   +4.36%     
==========================================
  Files          33       39       +6     
  Lines         276      306      +30     
==========================================
+ Hits           52       71      +19     
- Misses        224      235      +11     

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