Use Gemfile instead of Gem::Specification#add_development_dependency #1117

Job	Run time
ruby-versions / Generate Ruby versions	3s
build (2.7 / ubuntu-latest)	51s
build (2.7 / macos-latest)	1m 16s
build (3.0 / ubuntu-latest)	36s
build (3.0 / macos-latest)	1m 47s
build (3.1 / ubuntu-latest)	39s
build (3.1 / macos-latest)	50s
build (3.2 / ubuntu-latest)	37s
build (3.2 / macos-latest)	51s
build (3.3 / ubuntu-latest)	32s
build (3.3 / macos-latest)	58s
build (head / ubuntu-latest)	29s
build (head / macos-latest)	55s
	10m 24s

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