Prepare release v9.1.0 #2

Job	Run time
Perform checks before releasing	6s
tests (ubuntu-latest, 2.7)	1m 1s
tests (ubuntu-latest, 3.0)	50s
tests (ubuntu-latest, 3.1)	1m 1s
tests (ubuntu-latest, 3.2)	51s
tests (macos-latest, 2.7)	2m 11s
tests (macos-latest, 3.0)	1m 30s
tests (macos-latest, 3.1)	2m 5s
tests (macos-latest, 3.2)	1m 45s
tests (windows-latest, 2.7)	5m 6s
tests (windows-latest, 3.0)	4m 53s
tests (windows-latest, 3.1)	5m 41s
tests (windows-latest, 3.2)	5m 34s
tests (ubuntu-latest, jruby-9.4)	9m 6s
Publish Ruby Gem	9s
Create GitHub Release and Git tag	15s
	42m 4s

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