CI: Switch to plain Alpine image with modern ansible-lint

This also enables GitLab-parseable ansible-lint output.

Cf. common!26 (merged)

This also removes two unsupported and obsolete roles, as well as fixing a few (minor) issues along the way.

.ansible-lint

-parseable: true
-quiet: true
+---
+
 use_default_rules: true
+warn_list:
+  - experimental
+  - jinja[spacing]
+  - fqcn[action-core]
+  - fqcn[action]
+  - name[casing]
+  - name[missing]
+
 skip_list:
-  - '204'  # line length is checked by yamllint
-  - '401'  # git checkout must contain explicit version
-  - '701'  # 7xx is about ansible galaxy guidelines
-  - '702'
-  - '703'
+  - role-name