CI

Change GitHub CI to update checkout action to version 4 #80

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Run time

Learn about OS # on GitHub Actions

Job	Run time
Ruby 2.0	13s
Ruby 2.1	14s
Ruby 2.3	19s
Ruby 2.4	19s
Ruby 2.5	21s
Ruby 2.6	22s
Ruby 3.0	8s
Ruby 3.1	10s
Ruby 3.2	11s
Ruby 3.3	11s
Ruby ruby-head	8s
Ruby jruby-9.2	51s
Ruby jruby-9.3	37s
Ruby jruby-9.4	38s
Ruby jruby-head	41s
Ruby truffleruby-head	31s
Ruby 2.2	26s
Ruby 2.7	22s
	6m 42s