ci(php): pin supported PHP version

[WaterWhisperer]

Which issue does this PR close?

Closes #3305

Rationale

The PHP SDK action used distro/default PHP packages, so the tested PHP version could drift with runner image defaults.

What changed?

The PHP setup now installs explicit PHP 8.3 packages and exports the exact php8.3 / php-config8.3 binaries for later steps.

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.64%. Comparing base (aa8b719) to head (40e3ae7).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3333      +/-   ##
============================================
+ Coverage     73.57%   73.64%   +0.07%     
  Complexity      943      943              
============================================
  Files          1222     1223       +1     
  Lines        114939   115710     +771     
  Branches      91676    92476     +800     
============================================
+ Hits          84561    85214     +653     
- Misses        27532    27590      +58     
- Partials       2846     2906      +60     

Components	Coverage Δ
Rust Core	74.66% <ø> (+0.11%)	⬆️
Java SDK	58.44% <ø> (ø)
C# SDK	69.43% <ø> (-0.50%)	⬇️
Python SDK	81.06% <ø> (ø)
Node SDK	91.53% <ø> (ø)
Go SDK	40.20% <ø> (ø)
see 30 files with indirect coverage changes

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[hubcio]

@countradooku mind checking this?

[countradooku]

@countradooku mind checking this?

I will check

[countradooku]

@hubcio looks good to me