Add flag -Mnovect for compiling test/dt_arith.c (#6415)

* Added  CMAKE_CFLAGS="-Mnovect" for the workflow with nvhpc 26.3.0 where the issue occurs instead of editing CMake code specifically for test/dt_arith.c that would be applied to all nvhpc versions.

Author: lrknox

.github/workflows/nvhpc.yml

@@ -78,6 +78,7 @@ jobs:
           -DHDF5_BUILD_JAVA:BOOL=OFF \
           -DMPIEXEC_MAX_NUMPROCS:STRING="2" \
           -DMPIEXEC_PREFLAGS:STRING="--mca;opal_warn_on_missing_libcuda;0" \
+          -DCMAKE_C_FLAGS="-Mnovect" \
           $GITHUB_WORKSPACE
 
       - name: Build