test: skip task for starting maintenance services

tasks/rosetta/configure_maintenance.yml

@@ -33,3 +33,6 @@
       state: "stopped"
     - name: "rosetta_maintenance_begin.timer"
     - name: "rosetta_maintenance_end.timer"
+  # Don't test the task in Molecule; it cannot work, because the
+  # exlibris.service unit doesn't exist in the Molecule VM.
+  tags: [molecule-notest]