chore: group Dependabot updates

[marandaneto]

💡 Motivation and Context

Dependabot currently opens separate pull requests for each Cargo dependency and GitHub Actions update. Grouping updates reduces the number of maintenance pull requests.

💚 How did you test it?

• Parsed .github/dependabot.yml as YAML.
• Verified that the Cargo group and GitHub Actions group each use the "*" pattern.
• Ran git diff --check.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file

[greptile-apps]

_{Reviews (1): Last reviewed commit: "chore: group Dependabot updates" | Re-trigger Greptile}

[greptile-apps]

_{Reviews (2): Last reviewed commit: "chore: group Dependabot updates" | Re-trigger Greptile}