CI: Add a runner (MinGW/UCRT64) that builds without Fortran compiler.

[mmuetzel]

The CLANG32 (that is now failing and has been removed) checked if SuiteSparse could be built successfully in the absence of a Fortran compiler.

This PR adds a new runner that installs a build environment where the Fortran compiler is omitted (on purpose).

The UCRT64 environment of MSYS2 uses a GNU toolchain (GCC, GNU ld, libstdc++, ...) that links against the (newer) C runtime of Windows called UCRT (Universal CRT). The latter is the main difference to the MINGW64 environment which links against the (traditional) MSVCRT.
See: https://www.msys2.org/docs/environments/

[DrTimothyAldenDavis]

So this test should bypass the failing CLANG32, while at the same time testing the no-Fortran case, right?

[DrTimothyAldenDavis]

If that's my understanding then that's a good idea to add -- thanks.