[26.0] Replaced deprecated actions with modern equivalents

[ksuderman]

Replaces deprecated actions in the build job:

1. actions-hub/docker/login@master (quay.io + DockerHub logins) replaced with docker/login-action@v3 - the same action already used by the ghcrbuild job
2. Manual docker build + actions-hub/docker@master push replaced with docker/build-push-action@v6 - builds and pushes in one step
3. Added docker/setup-buildx-action@v3 - required by build-push-action

What changed functionally:

• The main galaxy-min image is now built and pushed to both DockerHub and quay.io in a single build-push-action step (instead of separate build + 2 push commands)

• The auto-expiring galaxy-k8s-auto per-commit image writes a temp Dockerfile and uses build-push-action to build and push it with the quay.expires-after=90d label

• All the same images are pushed to the same registries with the same tags

  The ghcrbuild job was already using these modern actions, so no changes were needed there.

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[mvdbeek]

Thanks @ksuderman!