Remove support for Ruby 2.7 #635

Job	Run time
nixfmt	14s
rubocop	11s
yard	8s
rspec-matrix (3.0, 3.5)	44s
actionlint	4s
rspec-matrix (3.0, 3.6)	54s
rspec-matrix (3.0, 3.7)	47s
rspec-matrix (3.0, 3.8)	49s
rspec-matrix (3.0, 3.9)	43s
rspec-matrix (3.0, 3.10)	59s
rspec-matrix (3.0, 3.11)	1m 8s
rspec-matrix (3.0, 3.12)	42s
rspec-matrix (3.1, 3.5)	59s
rspec-matrix (3.1, 3.6)	59s
rspec-matrix (3.1, 3.7)	1m 2s
rspec-matrix (3.1, 3.8)	46s
rspec-matrix (3.1, 3.9)	46s
rspec-matrix (3.1, 3.10)	54s
rspec-matrix (3.1, 3.11)	50s
rspec-matrix (3.1, 3.12)	1m 5s
rspec-github-workflow-wrapup-helper	1s
collate-coverage	10s
rspec	1s
	14m 56s

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