Update phpstan/phpstan requirement from 1.12.8 to 1.12.9 #1538

Job	Run time
PHP Lint (7.2)	21s
PHP Lint (7.3)	19s
PHP Lint (7.4)	16s
PHP Lint (8.0)	23s
PHP Lint (8.1)	22s
PHP Lint (8.2)	22s
PHP Lint (8.3)	21s
PHP Lint (8.4)	33s
Static Analysis (composer:normalize, 8.3)	20s
Unit tests (7.2)	27s
Static Analysis (php:fixer, 8.3)	25s
Unit tests (7.3)	12s
Static Analysis (php:stan, 8.3)	20s
Unit tests (7.4)	34s
Static Analysis (php:rector, 8.3)	34s
Unit tests (8.0)	19s
Unit tests (8.1)	23s
Unit tests (8.2)	27s
Unit tests (8.3)	14s
Unit tests (8.4)	20s
	7m 32s

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