[Fortran] Dsiable the declare-variant-6.f90 test for now (#448) * Revert "[Fortran] declare-variant-6 is now passing after LLVM's PR #206988 (#447)" This reverts commit 156201019953cae49cb475c36a01973bad7f891a. * [Fortran] Dsiable the declare-variant-6.f90 test for now