Add a CI job running on PHP 8.5 #125

Job	Run time
Static analysis	22s
Check composer.json	12s
Tests (7.2)	24s
Tests (8.0)	20s
Tests (7.3)	26s
Tests (7.4)	23s
Tests (8.1)	28s
Tests (8.2)	26s
Tests (8.3)	31s
Tests (8.4)	24s
Tests (8.4, dev)	24s
Tests (8.5)	28s
Tests (7.2, --prefer-lowest --prefer-stable, weak)	31s
	5m 19s

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