test(dcop): skip if basic invocation errors out

It's highly unlikely that a DCOP server would be running in containers.

Author: scop

test/t/test_dcop.py

@@ -2,6 +2,8 @@
 
 
 class TestDcop:
-    @pytest.mark.complete("dcop ", require_cmd=True)
+    @pytest.mark.complete(
+        "dcop ", require_cmd=True, skipif="! dcop &>/dev/null"
+    )
     def test_1(self, completion):
         assert completion