ci: harden release workflows (SHA-pin actions, least-privilege token, TLS timestamper) - #64

This Dependabot configuration does not set a cooldown period. Newly published packages can be malicious or unstable. Add a cooldown block with default-days: 7 to each package-ecosystem entry under updates to wait 7 days before proposing updates to newly published package versions. Reference: https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#cooldown