Regression with netCDF-Fortran test ftst_vars

[WardF]

Commit f1a3a64 appears to have caused a regression in netcdf-fortran, insofar as ftst_vars is now failing when linking against subsequent versions of libnetcdf-c. More investigation is needed, but the fix will include adding checks for such regressions back in to the netcdf-c CI. We will also need to re-wire main back into the netCDF-Fortran; I am removing it from the netCDF-Fortran CI for the moment so that Unidata/netcdf-fortran#418 will pass (correcting an issue in nf-config).

• Fix underlying issue.
• Add netcdf-c CI regression check
• Re-add main to netcdf-fortran CI.