Add `cooldown` settings for Dependabot #6790

Job	Run time
Ruby analysis (macos-latest, linked)	1m 14s
Ruby analysis (ubuntu-latest, nightly-latest)	50s
Ruby analysis (ubuntu-latest, default)	47s
Ruby analysis (macos-latest, default)	1m 28s
Ruby analysis (macos-latest, nightly-latest)	1m 3s
Ruby analysis (ubuntu-latest, linked)	50s
	6m 12s

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