QA: replace phpdbg in coverage target

[ohmyfelix]

Summary

• replace -p phpdbg with -p php in the coverage target of Makefile
• keep the existing coverage output split for GitHub Actions and local HTML generation

Motivation

Issue #73 tracks removing phpdbg from Contributte coverage targets. This repo still used phpdbg, so the coverage target now matches the new php-based pattern.

Changes

• update both coverage target variants in Makefile to run Tester with php

Testing

• make tests
• make coverage locally
• CI passes

Local coverage is currently blocked because this environment runs plain php without Xdebug, PCOV, or PHPDBG available for code coverage.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.19%. Comparing base (8350ceb) to head (b98ecfc).
⚠️ Report is 11 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (8350ceb) and HEAD (b98ecfc). Click for more details.

HEAD has 6 uploads less than BASE

Flag	BASE (8350ceb)	HEAD (b98ecfc)
	7	1

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #34      +/-   ##
==========================================
- Coverage   53.26%   48.19%   -5.07%     
==========================================
  Files          20       22       +2     
  Lines         276      249      -27     
==========================================
- Hits          147      120      -27     
  Misses        129      129              

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