Fortran: Fix check for F90 support

Since commit db76876db5 (Modules: Use new SOURCES_FROM_* try_compile
(1/2), 2022-09-26, v3.25.0-rc1~74^2~1) the variable containing the F90
code was named incorrectly.  Thus the compilation test was performed on
an empty source file.

Modules/CMakeTestFortranCompiler.cmake

@@ -65,7 +65,7 @@ endif()
 # Test for Fortran 90 support by using an f90-specific construct.
 if(NOT DEFINED CMAKE_Fortran_COMPILER_SUPPORTS_F90)
   message(CHECK_START "Checking whether ${CMAKE_Fortran_COMPILER} supports Fortran 90")
-  set(__TestCompiler_testFortranCompilerSource "
+  set(__TestCompiler_testFortranCompilerF90Source "
     PROGRAM TESTFortran90
     integer stop ; stop = 1 ; do while ( stop .eq. 0 ) ; end do
     END PROGRAM TESTFortran90