Add support for Symfony 8

[alexander-schranz]

Test current compatibility to Symfony 8.

Is required: FriendsOfSymfony/FOSHttpCache#597 as CI installs this package.

[alexander-schranz]

@Toflar CI seems currently be disabled. Github is doing this because there where not any changes and disable CI with schedules after 1-2 month:

psr6-symfony-http-cache-store/.github/workflows/ci.yaml

Lines 10 to 11 in 9b3eb5b

	schedule:
	- cron: 0 13 * * MON

You should be able reactivate it in: https://github.com/Toflar/psr6-symfony-http-cache-store/actions

[Toflar]

Re-enabled, I guess you need to push again to trigger CI?

[alexander-schranz]

@Toflar how would you handle the deprecation errors on lowest? As I added PHP 8.4:

Lot of Implicitly marking parameter like are shown:

Implicitly marking parameter $value as nullable is deprecated, the explicit nullable type must be used instead

[Toflar]

I guess that's a wrong configuration of phpunit because those are not deprecations we can influence, are they? So update the phpunit configuration, maybe?