Check (but not fix) Fortran format in GitHub actions

[climbfuji]

Check (but not fix) Fortran format in GitHub actions.

Note. The newly added GitHub actions workflow is currently failing intentionally to illustrate how the setup works. The temporary change to the Fortran source code that triggers this failure will be reverted so that all tests pass before this PR is merged.

This PR enables automated checking of the Fortran format using Codee in GitHub actions. The new test will fail if running Codee updates files that are modified in a pull request. The system tells the user to either run Codee locally (which is almost trivial when following the GitHub workflow) or applying a diff that the system produces.

This PR does not enable automatic reformatting and updates of pull requests, because this doesn't work if the pull request comes from a fork (which we usually require for the ccpp-framework repository). The stencil code to do this is submitted as comment in the current PR, however.

The checking is limited to the static Fortran source files in this repository, not the auto-generated Fortran code from capgen or prebuild - this will be addressed in a future PR.

While at it, I updated the existing GitHub workflows to run on develop only, since main is now frozen`, and to avoid concurrent workflow runs (i.e. cancel currently running tests from the same pull request if an update is pushed).

User interface changes?: No

Working toward #703

Testing:
test removed: n/a
unit tests: all pass
system tests: all pass (see note above about newly added test)
manual testing: n/a
test added: GitHub actions test to check formatting of static Fortran source files in this repository

[climbfuji]

Lines 4-5 will be removed before merging the PR, this will allow the newly added test to pass.