what happens if [jinja2:suite.rc] and [template variables] are both set.

[wxtim]

Describe the bug
Investigate what happens if [jinja2:suite.rc] and [template variables] are both set.

Steps to reproduce the bug

Uncompress rose-dep-warnings.tar.gz or manually create this workflow in ~/cylc-src/rose-dep-warnings:

rose-suite.conf:

[jinja2:suite.rc]
GREETING="Hello"
[template variables]
GREETING="Mittyn Da"

flow.cylc:

#!jinja2
[scheduling]
    initial cycle point = 1066
    [[dependencies]]
        R1 = foo
[runtime]
    [[foo]]
        script = echo {{ GREETING }}

Then run

cylc graph rose-dep-warnings
cylc install rose-dep-warnings
cylc play rose-dep-warnings
cat ~/cylc-run/rose-dep-warnings/log/flow-files/flow.processed.cylc

Expected behavior
A warning should be printed to the effect that you shouldn't use both sections.

Pull requests welcome!
This is an Open Source project - please consider contributing a bug fix
yourself (please read CONTRIBUTING.md before starting any work though).

[oliver-sanders]

cylc-rose should raise an error and refuse to work.