try comma-quoting CVMFSEXEC_REPOS, just in case

Author: matyasselmeci

tests/test_inside_gha.sh

@@ -219,7 +219,7 @@ case "$CVMFS_INSTALL" in
         ;;
     cvmfsexec)
         DOCKER_EXTRA_ARGS=(--privileged
-                           -e CVMFSEXEC_REPOS='oasis.opensciencegrid.org singularity.opensciencegrid.org'
+                           -e CVMFSEXEC_REPOS=oasis.opensciencegrid.org,singularity.opensciencegrid.org
                            -e CVMFSEXEC_DEBUG=true)
         ;;
 esac