Fixed a bug in the Gitlab CI (!30)

## What is the bug
The CMake option `IM_ENABLE_OPENACC` was by mistake written as `MS_ENABLE_OPENACC` in `gitlab-ci.yml`
## How do you fix it
Using the correct option now

Approved-by: Yen-Chen Chen <yen-chen.chen@tum.de>
Merged-by: Yen-Chen Chen <yen-chen.chen@tum.de>
Changelog: bugfix

.gitlab-ci.yml

@@ -74,7 +74,7 @@ nvhpc_gpu:
     - module load git gcc/11.2.0-gcc-11.2.0 nvhpc/22.5-gcc-11.2.0
     - mkdir nvhpc_gpu
     - cd nvhpc_gpu
-    - /sw/spack-levante/cmake-3.23.1-q5kzz6/bin/cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_C_COMPILER=nvc -DCMAKE_Fortran_COMPILER=nvfortran -DMS_ENABLE_OPENACC=ON
+    - /sw/spack-levante/cmake-3.23.1-q5kzz6/bin/cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_C_COMPILER=nvc -DCMAKE_Fortran_COMPILER=nvfortran -DIM_ENABLE_OPENACC=ON
     - make VERBOSE=1
     - make test
   tags: