Support PHP 8.4

PHP 8.4 is now in release candidate and due for release in about 6 weeks. Features are now sealed.

This pull request:

• Add PHP 8.4 tests in the GitHub Action
• Explicitly declares nullable parameters as nullable

Note: There is still a warning in relation to the GreedyCacheStrategy because the second argument ($defaultTtl) is required, but the first argument is optional. I'm not sure how you wish to resolve this so I'll defer to a separate issue. Options are to either stop the first argument (CacheStorageInterface $cache) from having a default value (but still allowing nullability), or to provide a default of the default ttl.

Thank you @andrewnicols for this PR.

I think that we can add a default value to defaultTtl. If we remove the default value to cache, this is potentially a breaking change.

Maybe something like 60.

Cheers,

I've set a default value in the constructor of 60. I was tempted to set the type hint (int) but that would be a breaking change so avoided that.

There are some errors with 8.4, lowest. Maybe we need to drop some versions on dependencies too?

Thanks @Kevinrob ,

I saw these the other day but didn't get a chance to trouble-shoot. I ended up having to reduce some alternate versions, but most of the existing lowest options were unsupported, and all of the highest version options were fully supported.

• phpunit/phpunit: 8.5.40 does seem to support PHP 8.4 but 9.6 also supports all versions so I felt it best to just bump the version
• symfony/phpunit-bridge: 5.4 does seem to support PHP 8.4 but 7.1.4 also supports all versions
• guzzlehttp/guzzle: Version 6.x is no longer maintained. Minimum version now needs to be 7.9.2 to proivde support for the required range of PHP versions
• guzzlehttp/promises: Version 1.x is no longer supported. Minimum version required is now 2.0.3
• guzzlehttp/psr7: Version 1.x is no longer maintained. Minimum version requireds is now 2.7.0