fix: test_shapes Polycone with ordered z-planes

DDTest/src/test_shapes.cc

@@ -20,7 +20,7 @@ int main(int /* argc */, char** /* argv */ ){
 
     // add single plane with addZPlanes
     dd4hep::Polycone polycone(0, 2*M_PI, {0, 0}, {1, 1}, {0, 1});
-    polycone.addZPlanes({0}, {1}, {0.5});
+    polycone.addZPlanes({0}, {1}, {2});
 
     // --------------------------------------------------------------------
   }