Adapt rules for PHP 8.1

[paulbalandan]

This change will target v4.5 once released.

[paulbalandan]

My question now is: should this branch off for a v2 release? @kenjis @MGatner

[kenjis]

No, it is not needed. Increment minor version number.
See https://medium.com/@sampart/semantic-versioning-when-you-change-the-required-programming-language-version-16a3a3555c95

[MGatner]

Agree with @kenjis: Compose will handle the language requirement and I don't see a need to maintain multiple styles branches with dedicated releases.

[paulbalandan]

I've created a new branch 1.8.x to house all related changes pending release of v4.5.