Maintenance/update ci

Updates CI to use Ubuntu-based runner. Revises environment_geoarray.yml.

added Maintenance label

assigned to @danschef

added 4 commits

• e31e96dc - Use Ubuntu-based CI runner and simplify docker file.
• ae28799b - Use conda where ever possible.
• d851b9f1 - Adapt .gitlab-ci.yml to Ubuntu-based CI.
• 109bf3f3 - Update HISTORY.rst.

Compare with previous version

This requires to fix #39 first.

Anyway, I merge this now to have the updated CI in place.

approved this merge request

marked this merge request as ready

mentioned in commit 6f4309de

merged