Added missing union type import #6742

Job	Run time
1/4	14m 43s
2/4	13m 43s
3/4	13m 35s
4/4	12m 22s
py-3-latest	18m 14s
flaky	6m 15s
_remote_background_indep_poll	5m 20s
_remote_background_indep_tcp	7m 33s
macos 1/5	20m 39s
macos 2/5	20m 9s
codecov	6s
	2h 12m 39s

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