PHP 8.4 deprecation fixes

[ghost]

• Fix PHP 8.4 parameter implicitly nullable deprecation
• Add basic static analysis to CI workflow with PHPStan
• Update GHA runner to one that is not retired

[goetas]

Nice! Thank you for this pr.

Is there a lot of work needed to increase the phpstan level?

[ghost]

Wasn't bad! I got up to level 6 by:

Level 2:

• Removing support for predis/predis ^0.8
• Removing some types that were removed in Symfony 5 (which is already a base requirement)

Level 3:

• Adding some missing return types to StorageInterface and property type to PhpRedis

Level 4:

• Updating PHPDoc to describe RateLimitService::$storage as nullable (which is already is, since it's untyped in PHP)

Level 5:

• Casting some numbers as strings where strings were expected

Level 6:

• Adding iterable type PHPDoc to NoxlogicRateLimitExtension::load() parameter $config (this was affecting SF 5.4 builds only)
• There are a lot more missing type errors that I didn't fix, but I generated a baseline to enforce strong typing in any new code.

[goetas]

Thank you for your excellent work

[ghost]

No problem! Would you mind releasing a 2.1.0 version please for folks who's like to squash PHP 8.4 deprecations?

[goetas]

Done