chore: Add Dependabot version-update cooldown #508

Job	Run time
test-platforms-and-versions (ubuntu-latest, 17)	3m 49s
test-platforms-and-versions (ubuntu-latest, 11)	4m 5s
test-platforms-and-versions (ubuntu-latest, 8)	3m 53s
test-contract-tests	4m 44s
test-platforms-and-versions (ubuntu-latest, 19)	3m 36s
test-packaging	5m 8s
	25m 15s

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