Update dependency phpstan/phpstan to v1.8.4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
phpstan/phpstan	require-dev	patch	1.8.3 -> 1.8.4

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Release Notes

phpstan/phpstan

v1.8.4

Compare Source

PHPStan 1.8.3 but faster!

Improvements 🔧

• Optimization: Degrade constant arrays if there's too many values recursively (phpstan/phpstan-src@0cc87f3, phpstan/phpstan-src@ec92402, phpstan/phpstan-src@13d6595), #​7918, #​7903, #​7901, #​7581
• Improve dead code detection after nested function calls with conditional never return type (#​1378), #​7188, thanks @​rvanvelzen!
• EnumCaseObjectType constructor made part of BC promise (phpstan/phpstan-src@1a8f070), #​7917

Bugfixes 🐛

• Fix ::class on string expression (#​1425), thanks @​rvanvelzen!
• Anonymous classes are final (phpstan/phpstan-src@a418c46), #​7904
• Result cache needs to be cleared after reportUnmatchedIgnoredErrors is changed (phpstan/phpstan-src@84852ab)
• Fix array_filter() that does not return all items (phpstan/phpstan-src@2e89a22), #​7909

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