Cylc 8 with LFRic Rose stems and Jinja2 issues

Jinja2 deprecated some old interfaces at version 3.0 (and added warning messages), they have removed back-support at version 3.1.

Cylc is currently sticking with Jinja2 v3.0.x in order to give everyone a chance to adapt to the Jinja2 warning messages. There’s more about the update here: