chore: use dependabot cooldowns

inspired by https://blog.yossarian.net/2025/11/21/We-should-all-be-using-dependency-cooldowns

docs: -  https://docs.github.com/en/code-security/reference/supply-chain-security/dependabot-options-reference#cooldown

example: https://github.com/python/cpython/blob/d8c56581560ed139d261dd14acd73597e40cf88b/.github/dependabot.yml#L19