[BUG] gha saving too much

[duncdrum]

Gh-actions is not playing nice with cypress, the caching seems to preserve a previous state of the exist container, which can lead to weird test failures.

rework the gha config files, to make them more robust

Context (please always complete the following information):

• OS: ubuntu 20.04
• eXist-db Version: :latest
• Java Version: 8
• App Version: dev5 head

[duncdrum]

to be clear we want layer caching of the :latest container, there should almost always be sufficient cause to download a newer container.