Inform about "no_push" in the logs

When using `no_push` it would be nice if at the end of building the image there was some text printed that informs the reader the image was built successfully but it is not pushed to a registry due to the `no_push` parameter.

Here is a log: https://github.com/szabgab/docker-perl-tester/actions/runs/21311387218/job/61348145470