Conditions to run docker CI pipelines

[KaruroChori]

Reported in here not to forget, as no specific decision has been taken

          >but maybe different filters are needed for docker.yml.

I reverted the change below in docker.yml. In theory, if it passes this test, there's no reason to trigger it for the other one. The build should have already been triggered by any changes here.. or not...

I dunno. Let me know what you think. Or we could avoid some thought and adjust later as needed.

Originally posted by @andy5995 in #13 (comment)