Mark RedisCluster method as impure

[VincentLanglet]

Similar to #4409

[ondrejmirtes]

Would you want to add something like @phpstan-all-methods-impure and pure above classes? It'd be more maintainable than this.

It'd still be possible to exclude a method and do the opposite above it.

[VincentLanglet]

Would you want to add something like @phpstan-all-methods-impure and pure above classes? It'd be more maintainable than this.

It'd still be possible to exclude a method and do the opposite above it.

Like this phpstan/phpdoc-parser#277 ?

[VincentLanglet]

Closing in favor of #4422