tests: Resolve Coverity RESOURCE_LEAK

In the error path need to unref the 'caps' as well
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>

tests/qemucaps2xmltest.c

@@ -113,6 +113,7 @@ testGetCaps(char *capsData, const testQemuData *data)
 
  error:
     virObjectUnref(qemuCaps);
+    virObjectUnref(caps);
     return NULL;
 }