FIX: add cache cleaning before installation

.gitlab-ci.yml

@@ -17,6 +17,7 @@ build_test:
   script:
     - git clone ${SPACK_REPO} -b ${SPACK_BRANCH}
     - . "./spack/share/spack/setup-env.sh"
+    - spack clean -a # Make sure spack doesn't have any caches left
     - spack env activate --without-view env/merlin/${SPACK_PCKG}
     - spack install -j ${MAX_JOB_NB} --add git-lfs
     - spack develop ${SPACK_SPEC}