[5.1] Add PHP 8.4 to CI

[phil-davis]

Part of issue #123

• add PHP 8.4 to CI
• chore: run cs-fixer regardless of PHP version (forcing it to run on PHP 8.4 in CI - it passes)
• explicitly mark nullable parameters like ?callback ?string. This was supported since PHP 7.1, so that is very convenient because the 5.1.x release series still supports all the way back to PHP 7.1

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.72%. Comparing base (2413496) to head (558d67f).
Report is 1 commits behind head on 5.1.

Additional details and impacted files

@@            Coverage Diff            @@
##                5.1     #126   +/-   ##
=========================================
  Coverage     99.72%   99.72%           
- Complexity      110      118    +8     
=========================================
  Files             7        7           
  Lines           365      365           
=========================================
  Hits            364      364           
  Misses            1        1           

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[phil-davis]

For these kind of changes, if someone was implementing this interface, and has string $eventName = null and we change this "underneath them" adding the ?, then will their code work unchanged?

LSP is not broken - the old and new interface, and the implementation of the interface all have exactly the same set of allowable things that can be passed in the parameter.

I wonder if this will break anything for anyone (e.g. in older versions of PHP) (callers will be fine - now it is explicit that they can pass null)

[cedric-anne]

I tested the following code in both PHP 7.4 and PHP 8.3 and it does not trigger any error.

interface TestI {
    public function test(?string $a = null);
}
class Cls implements TestI {
    public function test(string $a = null) {}
}

[phil-davis]

@cedric-anne IMO this will support PHP 8.4 for the 5.1.x series. Please review and comment.

Then I can check these things in master (which might already be OK), and try similar in other sabre-io repos.

[cedric-anne]

I tested the following code in both PHP 7.4 and PHP 8.3 and it does not trigger any error.

interface TestI {
    public function test(?string $a = null);
}
class Cls implements TestI {
    public function test(string $a = null) {}
}