Bump phpstan/phpstan from 1.12.2 to 1.12.3 #278

Job	Run time
Debug	1s
Check files / Changed	11s
XML Syntax	0s
Composer / Validation	13s
Code-QL / Analyze (javascript)	1m 45s
PHP CS / Default	4m 7s
PHP CS Fixer / Validation	3m 3s
PHP CS / Ecg	2m 10s
PHPStan / Analyze (ubuntu-latest, 7.4)	3m 13s
PHP CS / PhpCompatibility	5m 33s
PHPStan / Analyze (ubuntu-latest, 8.4)	2m 56s
Unit Tests (OpenMage)	0s
PHP Syntax	0s
	23m 12s

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