Add `cooldown` settings for Dependabot #6782

Job	Run time
Ruby analysis (ubuntu-latest, nightly-latest)	44s
Ruby analysis (ubuntu-latest, default)	44s
Ruby analysis (macos-latest, linked)	1m 9s
Ruby analysis (macos-latest, nightly-latest)	1m 1s
Ruby analysis (ubuntu-latest, linked)	46s
Ruby analysis (macos-latest, default)	1m 13s
	5m 37s

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