Update psalm/plugin-phpunit requirement from ^0.18.4 to ^0.19.0 #143

Job	Run time
PHP 8.1 on ubuntu-latest ()	18s
PHP 8.1 on ubuntu-latest (--prefer-lowest)	21s
PHP 8.1 on windows-latest ()	1m 46s
PHP 8.1 on windows-latest (--prefer-lowest)	1m 31s
PHP 8.1 on macOS-latest ()	1m 19s
PHP 8.1 on macOS-latest (--prefer-lowest)	1m 16s
PHP 8.2 on ubuntu-latest ()	20s
PHP 8.2 on ubuntu-latest (--prefer-lowest)	36s
PHP 8.2 on windows-latest ()	1m 10s
PHP 8.2 on windows-latest (--prefer-lowest)	58s
PHP 8.2 on macOS-latest ()	1m 43s
PHP 8.2 on macOS-latest (--prefer-lowest)	1m 57s
PHP 8.3 on ubuntu-latest ()	19s
PHP 8.3 on ubuntu-latest (--prefer-lowest)	21s
PHP 8.3 on windows-latest ()	59s
PHP 8.3 on windows-latest (--prefer-lowest)	1m 2s
PHP 8.3 on macOS-latest ()	2m 33s
PHP 8.3 on macOS-latest (--prefer-lowest)	2m 30s
	20m 59s

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