Fix MacOS tests on develop

The -u option allows to update the current head,
so tests won't fail if we are on develop

.github/workflows/macos_unit_tests.yaml

@@ -36,7 +36,7 @@ jobs:
     - name: Run unit tests
       run: |
         git --version
-        git fetch origin develop:develop
+        git fetch -u origin develop:develop
         . share/spack/setup-env.sh
         coverage run $(which spack) test
         coverage combine