bump MSRV to 1.64 #890

Job	Run time
Check Style	8s
semver	26s
features	50s
Check MSRV (1.64) on windows-latest	10m 4s
Check MSRV (1.64) on macos-latest	6m 43s
Check MSRV (1.64) on ubuntu-latest	6m 19s
Test beta on macos-latest	1m 8s
Test with Miri	1m 4s
Test stable on windows-latest	1m 57s
Test nightly on windows-latest	1m 25s
Test stable on macos-latest	55s
Test stable on ubuntu-latest	34s
Test nightly on ubuntu-latest	36s
Test beta on windows-latest	1m 32s
Test beta on ubuntu-latest	41s
Test nightly on macos-latest	59s
Build docs	20s
CI is green	3s
	35m 44s

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