chore(deps): update dependency phpstan/phpstan-phpunit to v0.12.21

This MR contains the following updates:

Package	Type	Update	Change
phpstan/phpstan-phpunit	require-dev	patch	0.12.20 -> 0.12.21

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Release Notes

phpstan/phpstan-phpunit

v0.12.21

Compare Source

• 6aaff11 - Add support for assertArrayHasKey (#​100)

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