Update .gitlab-ci.yml

.gitlab-ci.yml

-test:
+adios2-variable-problem:
   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc-12
   script:
+    - . /opt/spack/share/spack/setup-env.sh
     - spack env activate /opt/spack-environment/
     - spack load adios2
     - mkdir build