Updates to testing in SCM

[dustinswales]

The PR contains two changes:

• Here we introduce continuous integration tests to the ccpp-scm using GitHub workflows. There are two tests: The first CI test is a simple workflow that runs the ccpp_prebuild_config.py for the ccpp-scm, using the accompanying ccpp-physics. The second CI test goes further and runs the full SCM workflow, downloading and building dependencies and running the SCM regression-tests using the GNU compilers.
• There is also a change to the run_scm.py script when running with multiple cases. The input lists have been replaced by a list of python dictionaries, one for each run configuration.

[grantfirl]

@dustinswales I'll approve once https://github.com/dustinswales/ccpp-scm/pull/6 is merged.