Bump phpstan/phpstan from 1.12.16 to 2.1.6 #1794

Job	Run time
Pre run	3s
Lint: JS	1m 5s
Lint: CSS	0s
Lint: PHP	48s
Static Analysis: PHP	20s
Unit test: JS	1m 7s
E2E test: JS (1, 2)	5m 26s
E2E test: JS (2, 2)	5m 21s
Feature tests: PHP 7.4, WP latest	3m 9s
Feature tests: PHP 8.4, WP trunk	3m 3s
Unit test: PHP 8.0, WP latest	3m 7s
Feature tests: PHP 8.3, WP trunk	2m 56s
Unit test: PHP 8.4, WP trunk	3m 49s
Feature tests: PHP 8.2, WP trunk	2m 59s
Unit test: PHP 8.3, WP trunk	3m 14s
Feature tests: PHP 8.1, WP trunk	3m 12s
Unit test: PHP 8.2, WP trunk	3m 38s
Feature tests: PHP 8.0, WP latest	3m 13s
Unit test: PHP 8.1, WP trunk	3m 2s
Feature tests: PHP 7.4, WP 6.6	3m 12s
Unit test: PHP 8.0, WP trunk Multisite	2m 59s
Unit test (with coverage): PHP 8.0, WP latest	5m 4s
Unit test: PHP 8.0, WP latest , Testsuite: external-http	2m 48s
Unit test: PHP 7.4, WP latest Multisite	2m 54s
Unit test: PHP 7.4, WP latest , Testsuite: external-http	3m 11s
Unit test: PHP 7.4, WP 6.6	3m 12s
Unit test: PHP 7.4, WP 6.6 , Testsuite: external-http	3m 16s
	1h 16m 8s

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