Add `cooldown` settings for Dependabot #6791

Job	Run time
Ruby analysis (ubuntu-latest, default)	46s
Ruby analysis (macos-latest, nightly-latest)	1m 40s
Ruby analysis (macos-latest, default)	1m 53s
Ruby analysis (ubuntu-latest, linked)	49s
Ruby analysis (macos-latest, linked)	1m 28s
Ruby analysis (ubuntu-latest, nightly-latest)	52s
	7m 28s

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