Add "phpstan/extension-installer" to allowed plugins #96

Job	Run time
PHP 8.1, ubuntu-latest, prefer-lowest	13s
PHP 8.1, ubuntu-latest, prefer-stable	14s
PHP 8.1, macos-latest, prefer-lowest	1m 11s
PHP 8.1, macos-latest, prefer-stable	1m 10s
PHP 8.1, windows-latest, prefer-lowest	37s
PHP 8.1, windows-latest, prefer-stable	35s
PHP 8.2, ubuntu-latest, prefer-lowest	15s
PHP 8.2, ubuntu-latest, prefer-stable	11s
PHP 8.2, macos-latest, prefer-lowest	1m 11s
PHP 8.2, macos-latest, prefer-stable	1m 24s
PHP 8.2, windows-latest, prefer-lowest	39s
PHP 8.2, windows-latest, prefer-stable	39s
PHP 8.3, ubuntu-latest, prefer-lowest	15s
PHP 8.3, ubuntu-latest, prefer-stable	17s
PHP 8.3, macos-latest, prefer-lowest	1m 19s
PHP 8.3, macos-latest, prefer-stable	1m 12s
PHP 8.3, windows-latest, prefer-lowest	26s
PHP 8.3, windows-latest, prefer-stable	41s
PHP 8.4, ubuntu-latest, prefer-lowest	17s
PHP 8.4, ubuntu-latest, prefer-stable	11s
PHP 8.4, macos-latest, prefer-lowest	1m 19s
PHP 8.4, macos-latest, prefer-stable	1m 20s
PHP 8.4, windows-latest, prefer-lowest	30s
PHP 8.4, windows-latest, prefer-stable	35s
	16m 41s

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