Allow base-4.20, fixes #230 #251

Job	Run time
arm (arm32v7)	14s
build (ubuntu-latest, 8.6, 3.8.1.0)	6m 0s
arm (arm64v8)	14s
freebsd (self-hosted, FreeBSD, X64, 9.4.8)	2m 3s
darwin_arm (self-hosted, macOS, ARM64, 8.10.7)	1s
build (ubuntu-latest, 8.8, 3.8.1.0)	6m 20s
freebsd (self-hosted, FreeBSD, X64, 9.6.4)	2m 5s
build (ubuntu-latest, 8.10, 3.8.1.0)	6m 10s
darwin_arm (self-hosted, macOS, ARM64, 9.2.6)	1s
i386	3m 56s
build (ubuntu-latest, 9.0, 3.8.1.0)	6m 9s
darwin_arm (self-hosted, macOS, ARM64, 9.4.4)	1s
build (ubuntu-latest, 9.2, 3.8.1.0)	4m 29s
build (ubuntu-latest, 9.4, 3.8.1.0)	5m 10s
build (ubuntu-latest, 9.6, 3.8.1.0)	3m 46s
build (ubuntu-latest, 9.8, 3.8.1.0)	3m 37s
build (macOS-latest, 9.4, 3.8.1.0)	5s
build (macOS-latest, 9.6, 3.8.1.0)	5s
build (windows-latest, 9.4, 3.8.1.0)	11m 14s
build (windows-latest, 9.6, 3.8.1.0)	11m 16s
	1h 12m 56s

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