fix generics treating symchoice symbols as uninstantiated #26618

Job	Run time
ubuntu-20.04 (batch: allowed_failures)	7m 38s
ubuntu-20.04 (batch: 0_3)	20m 38s
ubuntu-20.04 (batch: 1_3)	27m 43s
ubuntu-20.04 (batch: 2_3)	22m 11s
macos-12 (batch: allowed_failures)	11m 14s
macos-12 (batch: 0_3)	37m 34s
macos-12 (batch: 1_3)	33m 21s
macos-12 (batch: 2_3)	27m 44s
	3h 8m 3s

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