Is your feature request related to a problem? Please describe.

At time the full CI is run even when only doc/howto_release.md is edited which does not require CI checks at all.
This is a waste of runner resources.

Describe the solution you'd like

Like in the GDAL repo, add support for [skip ci] or [ci skip].

Note: Once implemented, the contributor needs to carefully decide if their PR submission may skip CI or not (it will rather be an exception to skip it).