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Add a Makefile for Ruby/`bundle`/Jekyll commands that I always forget. #2268

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Run time

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Job	Run time
test macos-latest py3.13	32s
test macos-latest py3.12	39s
test ubuntu-latest py3.11	53s
test ubuntu-latest py3.13	45s
test windows-latest py3.12	1m 36s
test windows-latest py3.13	3m 3s
test windows-latest py3.11	2m 21s
test ubuntu-latest py3.12	52s
test macos-latest py3.11	28s
	11m 9s