Bump version to v3.8.1 #2018

Job	Run time
Rustfmt (stable)	11s
Build and Test (ubuntu-latest, 1.65)	2m 19s
clippy_check (ubuntu-latest, stable)	27s
Build and Test (ubuntu-latest, 1.70)	2m 6s
clippy_check (ubuntu-latest, nightly)	33s
clippy_check (windows-latest, stable)	1m 23s
Build and Test (ubuntu-latest, 1.75)	1m 54s
clippy_check (windows-latest, nightly)	1m 36s
Build and Test (ubuntu-latest, stable)	5m 57s
Build and Test (ubuntu-latest, beta)	1m 0s
Build and Test (ubuntu-latest, nightly)	2m 18s
Build and Test (windows-latest, 1.65)	3m 46s
Build and Test (windows-latest, 1.70)	2m 53s
Build and Test (windows-latest, 1.75)	2m 49s
Build and Test (windows-latest, stable)	3m 54s
Build and Test (windows-latest, beta)	3m 49s
Build and Test (windows-latest, nightly)	3m 52s
Tests result	1s
	40m 48s

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