Drop support for GHC < 8.6 #219

Job	Run time
i386	4m 50s
arm (arm32v7)	4m 19s
darwin_arm (self-hosted, macOS, ARM64, 8.10.7)	1m 4s
arm (arm64v8)	3m 9s
darwin_arm (self-hosted, macOS, ARM64, 9.2.6)	58s
darwin_arm (self-hosted, macOS, ARM64, 9.4.4)	1m 0s
build (ubuntu-latest, 8.6.5, 3.8.1.0)	5m 30s
build (ubuntu-latest, 8.8.4, 3.8.1.0)	5m 31s
build (ubuntu-latest, 8.10.7, 3.8.1.0)	5m 27s
build (ubuntu-latest, 9.0.2, 3.8.1.0)	5m 10s
build (ubuntu-latest, 9.2.7, 3.8.1.0)	3m 45s
build (ubuntu-latest, 9.4.5, 3.8.1.0)	4m 27s
build (ubuntu-latest, 9.6.1, 3.8.1.0)	4m 46s
build (macOS-latest, 9.4.5, 3.8.1.0)	21m 37s
build (macOS-latest, 9.6.1, 3.8.1.0)	19m 22s
build (windows-latest, 9.4.5, 3.8.1.0)	23m 29s
build (windows-latest, 9.6.1, 3.8.1.0)	15m 8s
	2h 9m 32s

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