Remove ignore of cs rule SlevomatCodingStandard.TypeHints.TypeHintDeclaration.UselessDocComment

[PeeHaa]

We currently cannot use the generics syntax on our Promise objects in the doc blocks resulting in:

17 | ERROR | [x] Method \HarmonyIO\Cache\Cache::exists() does not need documentation comment.
| | (SlevomatCodingStandard.TypeHints.TypeHintDeclaration.UselessDocComment)

Depends on slevomat/coding-standard#673