Update workflow for 8.4

[peterfox]

Changes In Code

Bumping workflows to use PHP 8.4

Issue ticket number / Business Case

Required to maintain project.

Checklist before requesting a review

• I have written PHPUnit tests.
• I have updated the documentation and opened a pull request within
  the feature flags documentation repo.
• I have checked code styles, PHPStan etc. pass.
• I have provided an issue/business case.
• I have added the enhancement label for a new feature.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.94%. Comparing base (6223858) to head (5e1d8f1).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #68      +/-   ##
============================================
+ Coverage     82.84%   82.94%   +0.09%     
- Complexity      202      203       +1     
============================================
  Files            31       31              
  Lines           548      551       +3     
============================================
+ Hits            454      457       +3     
  Misses           94       94              

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