chore(#11007): group github-actions version updates into one PR

[bc004346]

Description

Adds a groups entry to the github-actions ecosystem in .github/dependabot.yml so all GitHub Actions version updates are consolidated into a single pull request.

The github-actions ecosystem had no groups, so it inherited Dependabot's default open-pull-requests-limit: 5. With ~15 actions across the workflows, Dependabot fills its 5 open-PR slots and then stops opening new bumps — which is why action updates stopped appearing.

Reproduced in a fork by enabling Dependabot version updates and forcing runs (Insights → Dependency graph → Dependabot → Check for updates):

• Before: Dependabot opened exactly 5 individual github-actions PRs and stopped. A deliberately-outdated actions/checkout never got a PR — it was cut off by the 5-PR cap.
• After this change: the individual PRs were superseded by a single grouped PR containing all 15 outstanding action updates (checkout, docker/login-action, setup-buildx-action, configure-aws-credentials, etc.).

Closes: #11007

Code review checklist

• UI/UX backwards compatible: Test it works for the new design (enabled by default). And test it works in the old design, enable can_view_old_navigation permission to see the old design. Test it has appropriate design for RTL languages.
• Readable: Concise, well named, follows the style guide
• Documented: Configuration and user documentation on cht-docs
• Tested: Unit and/or e2e where appropriate
• Internationalised: All user facing text
• Backwards compatible: Works with existing data and configuration or includes a migration. Any breaking changes documented in the release notes.
• AI disclosure: Please disclose use of AI per the guidelines.

License

The software is provided under AGPL-3.0. Contributions to this project are accepted under the same license.

[github-actions]

All checks passed — thank you @bc004346! This PR is ready for review.

[mrjones-plip]

Thanks for jumping on this @bc004346 ! LGTM