Fix compilation in multi-version php environment

[rforced]

We have an environment where multiple versions of PHP is installed.

The default /usr/bin/php is PHP 8.5. In there is also /usr/bin/php84, 83, etc.

When you compile an app when the environment default is 8.5 (box is still broken on PHP 8.5),

php84 ./application app:build -vvv --build-version=0.1

Will still fail, because we don't pass the wanted php to box.

In RequirementsBuilder.php line 29:
                                                                            
  [ErrorException]                                                          
  Using null as an array offset is deprecated, use an empty string instead  
                                                                            

Exception trace:

This now passes the wanted php version to execute box with.
With this change, it will respect what version was "passed" in the command line. This also still works on Windows.

Please let me know if you have any questions.

[rforced]

@owenvoke test failure is unrelated to my PR

[rforced]

@owenvoke any chance you can look at this?

[owenvoke]

This makes sense to me. 👍🏻 I've actually considered doing this previously, and not too sure why I didn't. 🤔

[owenvoke]

Released as part of v12.1.0, thanks @rforced!