Remove phpdbg from coverage target

[ohmyfelix]

Summary

Switch the coverage target in Makefile from phpdbg to php so this repository matches the org-wide coverage runner update tracked in contributte/contributte#73.

Motivation

phpdbg is being removed from Contributte coverage targets. This keeps openapi aligned with that change and lets coverage run through the standard PHP binary when a supported coverage driver is available.

Changes

• replace -p phpdbg with -p php in both coverage target branches
• keep the existing coverage output behavior for local and GitHub Actions runs
• verify the regular test suite still passes after the Makefile change

Testing

• make tests
• make coverage (fails locally: PHP has no Xdebug or PCOV extension, so code coverage is unavailable with php in this environment)
• CI passes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.47%. Comparing base (03347a7) to head (529eecf).
⚠️ Report is 5 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (03347a7) and HEAD (529eecf). Click for more details.

HEAD has 9 uploads less than BASE

Flag	BASE (03347a7)	HEAD (529eecf)
	10	1

Additional details and impacted files

@@            Coverage Diff             @@
##           master       #6      +/-   ##
==========================================
- Coverage   92.98%   85.47%   -7.51%     
==========================================
  Files          26       27       +1     
  Lines         926      888      -38     
==========================================
- Hits          861      759     -102     
- Misses         65      129      +64     

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