Bump actions/checkout from 3 to 4 #16

Job	Run time
Rubocop linting	47s
NON-MRI: ubuntu-20.04 jruby	1m 33s
NON-MRI: ubuntu-20.04 jruby no SSL	1m 11s
NON-MRI: ubuntu-20.04 jruby-head	1m 29s
NON-MRI: ubuntu-20.04 truffleruby	1m 25s
NON-MRI: ubuntu-20.04 truffleruby-head	1m 21s
NON-MRI: macos-10.15 jruby	1s
NON-MRI: macos-10.15 truffleruby	1s
NON-MRI: macos-11 jruby	1m 22s
NON-MRI: macos-11 truffleruby	1m 31s
MRI: ubuntu-20.04 2.4	1m 0s
MRI: ubuntu-20.04 2.5	1m 24s
MRI: ubuntu-20.04 2.6	49s
MRI: ubuntu-20.04 2.7	46s
MRI: ubuntu-20.04 3.0	40s
MRI: ubuntu-20.04 3.1	39s
MRI: ubuntu-20.04 head	32s
MRI: ubuntu-18.04 2.2	1s
MRI: ubuntu-18.04 2.3	1s
MRI: ubuntu-18.04 2.4	1s
MRI: ubuntu-18.04 2.5	1s
MRI: ubuntu-18.04 2.6	1s
MRI: ubuntu-18.04 2.7	1s
MRI: ubuntu-18.04 3.0	1s
MRI: ubuntu-18.04 3.1	1s
MRI: ubuntu-18.04 head	1s
MRI: macos-10.15 2.2	1s
MRI: macos-10.15 2.3	1s
MRI: macos-10.15 2.4	1s
MRI: macos-10.15 2.5	1s
MRI: macos-10.15 head	1s
MRI: macos-11 2.5	1m 55s
MRI: macos-11 2.6	1m 13s
MRI: macos-11 2.7	1m 21s
MRI: macos-11 3.0	45s
MRI: macos-11 3.1	42s
MRI: macos-11 head	42s
MRI: windows-2022 2.2	3m 28s
MRI: windows-2022 2.3	3m 43s
MRI: windows-2022 2.4	3m 44s
MRI: windows-2022 2.5	4m 6s
MRI: windows-2022 2.6	2m 15s
MRI: windows-2022 2.7	1m 56s
MRI: windows-2022 3.0	2m 5s
MRI: windows-2022 3.1	2m 34s
MRI: windows-2022 ucrt	1m 42s
MRI: windows-2022 mswin	2m 13s
MRI: windows-2022 2.7 no SSL	2m 10s
MRI: ubuntu-20.04 head yjit	36s
MRI: ubuntu-20.04 2.7 no SSL	52s
MRI: ubuntu-22.04 3.1	29s
MRI: ubuntu-22.04 head	28s
	55m 44s

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