Make dependabot update github actions by making changes in dependabot.yml

Fixes

Fixes #1046 by @krysal

Description

Some GH action dependencies are behind the latest updates:

actions/setup-python in CI + CD / Lint job

docker/setup-buildx-action in CI + CD / Build images (ingestion_server) job

etc.

To keep them updated via dependabot, changes in the dependabot.yml is made.

Checklist

[x] My pull request has a descriptive title (not a vague title like Update index.md).
[x] My pull request targets the default branch of the repository (main) or a parent feature branch.
[x] My commit messages follow [best practices][best_practices].
[x] My code follows the established code style of the repository.

[best_practices]: https://git-scm.com/book/en/v2/Distributed-Git-Contributing-to-a-Project#_commit_guidelines

Developer Certificate of Origin

``` Developer Certificate of Origin Version 1.1 Copyright (C) 2004, 2006 The Linux Foundation and its contributors. 1 Letterman Drive Suite D4700 San Francisco, CA, 94129 Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. Developer's Certificate of Origin 1.1 By making a contribution to this project, I certify that: (a) The contribution was created in whole or in part by me and I have the right to submit it under the open source license indicated in the file; or (b) The contribution is based upon previous work that, to the best of my knowledge, is covered under an appropriate open source license and I have the right under that license to submit that work with modifications, whether created in whole or in part by me, under the same open source license (unless I am permitted to submit under a different license), as indicated in the file; or (c) The contribution was provided directly to me by some other person who certified (a), (b) or (c) and I have not modified it. (d) I understand and agree that this project and the contribution are public and that a record of the contribution (including all personal information I submit with it, including my sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved. ```

WordPress / openverse-api