Update CI to fix OSX jobs

.gitlab-ci.yml

@@ -55,7 +55,7 @@ update-osx:
     - source /Users/ci/Miniconda3/etc/profile.d/conda.sh  # source conda activation script
     - conda activate base
     - conda list                                         # list conda packages in environment for debugging purposes
-    - conda install -c default "xz>=5, <6" libarchive  # Install specific compatible versions
+    - conda install -c conda-forge -c default "xz>=5, <6" libarchive  # Install specific compatible versions
     - conda update -c default conda
     - conda update -c default conda-build
     - conda list                                         # list conda packages in environment for debugging purposes