Add v0.8.x to the CI #346

Job	Run time
TestPoll	30s
Test (ubuntu-latest)	49s
TestWakerPipe	30s
Test (macos-latest)	1m 46s
CheckTargets	1m 9s
Test (windows-latest)	1m 33s
Check (armv7-sony-vita-newlibeabihf)	28s
Clippy	11s
Docs	13s
Check (sparcv9-sun-solaris)	30s
Check (x86_64-pc-solaris)	29s
MinimalVersions (ubuntu-latest)	22s
MSRV (ubuntu-latest)	2m 0s
MinimalVersions (macos-latest)	52s
Nightly	25s
MSRV (windows-latest)	2m 9s
MinimalVersions (windows-latest)	40s
Rustfmt	8s
Sanitizer (address)	1m 9s
Sanitizer (leak)	49s
Sanitizer (memory)	1m 49s
Sanitizer (thread)	54s
Passed	1s
	19m 26s

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