Add phpstan to github action #26

Job	Run time
Prepare system tests	50s
Install PHP dependencies	23s
Install JS/CSS dependencies and build assets	43s
Check Javascript code style	45s
Check PHP code style	1m 22s
Check CSS code style	34s
Run Unit tests (8.1)	27s
Run Unit tests (8.4)	29s
Run PHPstan	1m 48s
Run Unit tests (8.3)	24s
Run integration tests (8.2, phpunit.xml.dist)	47s
Run integration tests (8.3, phpunit-pgsql.xml.dist)	42s
Run Unit tests (8.2)	29s
Run integration tests (8.1, phpunit-pgsql.xml.dist)	42s
Run integration tests (8.4, phpunit.xml.dist)	50s
Run integration tests (8.4, phpunit-pgsql.xml.dist)	45s
Run integration tests (8.1, phpunit.xml.dist)	40s
Run integration tests (8.2, phpunit-pgsql.xml.dist)	50s
Run integration tests (8.3, phpunit.xml.dist)	54s
Run system tests (8.4, cmysqlmax, mysqli, mysql)	11m 20s
Run system tests (8.1, cpostgres, pgsql, postgres)	12m 5s
Run system tests (8.1, cpostgres, pgsql, postgres)	11m 43s
Run system tests (8.4, cpostgresmax, pgsql, postgres)	12m 20s
	1h 1m 52s

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