ci: add dependabot configuration for actions, npm, and bundler

[Copilot]

Adds automated dependency management for GitHub Actions, npm packages, and Ruby gems with auto-merge for safe updates.

Configuration

.github/dependabot.yml

• Daily updates for github-actions, npm, and bundler ecosystems
• Groups vitest packages (*vitest*) to avoid fragmented PRs
• Limits to 10 open PRs per ecosystem

.github/workflows/dependabot-auto-merge.yml

• Auto-merges patch and minor version updates from Dependabot
• Requires CI checks to pass before merge
• Uses dependabot/fetch-metadata@v2 for update type detection

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• spec.openapis.org
  • Triggering command: node (vitest 2) (dns block)
  • Triggering command: node (vitest 1) (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>ci: add a dependabot configuration </issue_title>
<issue_description>Since this repository is using GitHub actions, nom and gem, it should have a dependabot configuration for the 3 package managers.
Npm should have a group for the vitest deps.
Lastly, we could also bring the auto merge workflow</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes ci: add a dependabot configuration  #146

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[ralfhandl]

Looks good, never used it for Ruby gems before.