fix phpstan usage of deprecated FileSystemInterface::EXISTS_REPLACE o… #145

Job	Run time
Tests (9.5, entity_to_text)	1m 16s
Upgrade Status (9.5, entity_to_text)	1m 40s
Tests (10.0, entity_to_text)	1m 6s
Functional Tests (9.5, entity_to_text)	1m 44s
Functional Tests (10.0, entity_to_text)	1m 32s
Tests (10.1, entity_to_text)	1m 2s
Functional Tests (10.1, entity_to_text)	1m 22s
Tests (10.2, entity_to_text)	1m 3s
Functional Tests (10.2, entity_to_text)	1m 25s
	12m 10s

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