Update dependency slevomat/coding-standard to v8.12.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
slevomat/coding-standard	require-dev	minor	8.11.1 -> 8.12.0

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Release Notes

slevomat/coding-standard

### [`v8.12.0`](https://togithub.com/slevomat/coding-standard/releases/tag/8.12.0) [Compare Source](https://togithub.com/slevomat/coding-standard/compare/8.11.1...8.12.0) ## 🆕 New sniffs - `SlevomatCodingStandard.Arrays.ArrayAccess`: Disallow whitespace between array access operator and the variable, or between array access operators (thanks to [@​kamil-zacek](https://togithub.com/kamil-zacek)) ## 🐛 Fixes - `SlevomatCodingStandard.Classes.ClassStructure`: Fixed fixer - `SlevomatCodingStandard.ControlStructures.RequireNullSafeObjectOperator`: Fixed false positive - `SlevomatCodingStandard.Namespaces.ReferenceUsedNamesOnly`: Fixes - `SlevomatCodingStandard.Arrays.DisallowPartiallyKeyed`: Fixed false positive

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