Add typeguards to `contains` methods #14692

Job	Run time
stubtest: stdlib (ubuntu-latest, 3.12)	40s
stubtest: stdlib (ubuntu-latest, 3.11)	38s
stubtest: stdlib (windows-latest, 3.11)	1m 46s
stubtest: stdlib (windows-latest, 3.10)	1m 15s
stubtest: stdlib (windows-latest, 3.12)	1m 16s
stubtest: stdlib (windows-latest, 3.13)	1m 6s
stubtest: stdlib (windows-latest, 3.14)	1m 14s
stubtest: stdlib (ubuntu-latest, 3.14)	36s
stubtest: stdlib (macos-latest, 3.12)	22s
stubtest: stdlib (ubuntu-latest, 3.13)	38s
stubtest: stdlib (ubuntu-latest, 3.10)	52s
stubtest: stdlib (macos-latest, 3.10)	48s
stubtest: stdlib (macos-latest, 3.13)	23s
stubtest: stdlib (macos-latest, 3.14)	26s
stubtest: stdlib (macos-latest, 3.11)	33s
	12m 33s

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