Update PHPStan packages

This MR contains the following updates:

Package	Type	Update	Change
phpstan/phpstan	require-dev	patch	1.12.14 -> 1.12.15
phpstan/phpstan-symfony	require-dev	patch	1.4.12 -> 1.4.13

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Release Notes

phpstan/phpstan (phpstan/phpstan)

v1.12.15

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Bugfixes 🐛

• Fix inferring type of new with generic type with constructor in parent class (https://github.com/phpstan/phpstan-src/commit/a063119ee422460615adaa7a37bc4c5d2e755971), #​8219, #​2735
• Support tagged unions in array_merge (#​3770), #​7857, #​8632, #​9559, thanks @​herndlm!

Internals 🔍

• Cleanup instanceof ConstantBooleanType checks (#​3771), thanks @​staabm!

phpstan/phpstan-symfony (phpstan/phpstan-symfony)

v1.4.13

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• dd1aaa7 - Support for Messenger HandleTrait return types
• 1ef4dce - Merge remote-tracking branch 'origin/1.4.x' into 2.0.x
• 55ff7b7 - Merge remote-tracking branch 'origin/1.4.x' into 2.0.x
• 282a698 - Fix after PHPStan update
• bb3e671 - Cleanup skipCheckGenericClasses
• 237165e - Fixes after PHPStan update
• d1e08ac - Fixes after PHPStan update
• a0572ad - Fixes after PHPStan update
• 7e5633f - [BCB] Remove legacy config options with _ in their name
• 4f260f0 - Merge remote-tracking branch 'origin/1.4.x' into 2.0.x
• 3eb61a0 - Fixes after PHPStan update
• bd9efb7 - Fixes after PHPStan update
• 23a776d - Fixes after TypeSpecifier BC break
• c88f96e - Drop dependency on nikic/php-parser
• 90e8976 - Update build-cs
• 2f736a6 - Stop testing PHP 7.2 and 7.3
• 2c53b38 - Open 2.0.x

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