Update dependency phpstan/phpstan to v1.8.4

This MR 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 (https://github.com/phpstan/phpstan-src/commit/0cc87f37855611868d784deb3d5ec26c5058fda4, https://github.com/phpstan/phpstan-src/commit/ec9240294a85e84fc212f551c92698e6005cf3c1, https://github.com/phpstan/phpstan-src/commit/13d659522cf2b24c12e14183e8932e8f7270bcd3), #​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 (https://github.com/phpstan/phpstan-src/commit/1a8f07040d37a68e612a771e67322e8f624ae6aa), #​7917

Bugfixes 🐛

• Fix ::class on string expression (#​1425), thanks @​rvanvelzen!
• Anonymous classes are final (https://github.com/phpstan/phpstan-src/commit/a418c461fab8f118f99b2f6e1e72fd07a4800e1d), #​7904
• Result cache needs to be cleared after reportUnmatchedIgnoredErrors is changed (https://github.com/phpstan/phpstan-src/commit/84852ab8d9d4cbe3939d6f55e48e20f0481c3166)
• Fix array_filter() that does not return all items (https://github.com/phpstan/phpstan-src/commit/2e89a22dc28a044b65dc8f2bf7c76fd0b65f66ee), #​7909

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