[TASK] Allow `assertInstanceOf` calls in tests (#1377) #2319

Job	Run time
Composer Validate (8.3)	7s
PHP Lint (7.3)	7s
PHP Lint (7.4)	8s
PHP Lint (8.0)	10s
PHP Lint (8.1)	8s
PHP Lint (8.2)	10s
PHP Lint (8.3)	8s
PHP Lint (8.4)	10s
Static Analysis (composer:normalize, 8.3)	18s
Unit tests (7.3, lowest)	14s
Unit tests (7.3, highest)	17s
Static Analysis (php:fixer, 8.3)	21s
Static Analysis (php:md, 8.3)	18s
Unit tests (7.4, lowest)	14s
Static Analysis (php:rector, 8.3)	20s
Unit tests (7.4, highest)	18s
Unit tests (8.0, lowest)	19s
Static Analysis (php:stan, 8.3)	35s
Unit tests (8.0, highest)	17s
Unit tests (8.1, lowest)	14s
Unit tests (8.1, highest)	11s
Unit tests (8.2, lowest)	13s
Unit tests (8.2, highest)	13s
Unit tests (8.3, lowest)	14s
Unit tests (8.3, highest)	16s
Unit tests (8.4, lowest)	14s
Unit tests (8.4, highest)	14s
	6m 28s

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