Guarantee level_override exists #153

Job	Run time
ruby-versions / Generate Ruby versions	1s
build (2.5 / ubuntu-latest)	20s
build (2.5 / windows-latest)	3m 13s
build (2.6 / ubuntu-latest)	22s
build (2.6 / macos-latest)	26s
build (2.6 / windows-latest)	3m 31s
build (2.7 / ubuntu-latest)	23s
build (2.7 / macos-latest)	23s
build (2.7 / windows-latest)	1m 48s
build (3.0 / ubuntu-latest)	6s
build (3.0 / macos-latest)	9s
build (3.0 / windows-latest)	54s
build (3.1 / ubuntu-latest)	17s
build (3.1 / macos-latest)	10s
build (3.1 / windows-latest)	1m 37s
build (3.2 / ubuntu-latest)	8s
build (3.2 / macos-latest)	8s
build (3.2 / windows-latest)	47s
build (3.3 / ubuntu-latest)	6s
build (3.3 / macos-latest)	7s
build (3.3 / windows-latest)	2m 15s
build (head / ubuntu-latest)	9s
build (head / macos-latest)	10s
build (head / windows-latest)	1m 22s
	18m 52s

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