CI: Activate "enable-fortran" in our CI tests

[holke]

Feature request

Is your feature request related to a problem? Please describe.
We are currently adding a fortran interface. With #1182 we now have a configure option "--enable-fortran" and a CMake option should follow.
These are currently not tested in our CI, which also excludes all possible future Fortran related test cases.

Describe the solution or feature you'd like
Test the "enable-fortran" option in our CI.
I would suggest adding it to all test cases by default.

Should we also consider testing one version with "disable-fortran"?

Describe alternatives you've considered
Not testing is not an option.

Estimated priority
Which of these is most applicable (remove the others):

"Priority: medium" Should be solved within half a year

Additional context

[Davknapp]

I think @sandro-elsweijer is already on it

[holke]

Yes, havent seen that before. I guess #1204 will adress this.

[sandro-elsweijer]

@holke I already implemented it for the CMake build system, but there the cmake flag is not yet implemented. I will not implement it for the autotools CI.