[TASK] Use `ghcr.io` core-testing images in non-ci context

The docker container image hub is slowly becoming more
and more problematic for open source organisations, it's
time to move to another container registry for core-testing
images. Images are now build and published to both Docker
HUB and GitHub Container Registry (`ghcr.io`).

To test the ghcr.io images, the patch changes runTests.sh
to use them them for local (non CI) execution already.

We can not fully switch to ghcr.io yet, since CI uses the
docker registry container as mirror for images to heavily
reduce network load and increase performance. The registry
container however can only mirror hub.docker.io images, so
we need a different solution for CI first. When this is
done, we'll stop uploading images to docker hub later.

Resolves: #100617
Releases: main, 11.5, 10.4
Change-Id: Ia309826618696dc25b15527b73fa704235285479
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78668


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk...