fix deprecated warning QSet<T> QList<T>::toSet()

Use
QSet<T>(list.begin(), list.end())
instead.

This function was introduced in Qt 5.14

sources/qetgraphicsitem/conductor.cpp

@@ -1639,7 +1639,11 @@ QSet<Conductor *> Conductor::relatedPotentialConductors(const bool all_diagram,
 			for (Conductor *c : other_conductors_list_t) {
 				other_conductors += c->relatedPotentialConductors(all_diagram, t_list);
 			}
+#if QT_VERSION < QT_VERSION_CHECK(5, 14, 0)	// ### Qt 6: remove
 			other_conductors += other_conductors_list_t.toSet();
+#else
+			other_conductors += QSet<Conductor*>(other_conductors_list_t.begin(),other_conductors_list_t.end());
+#endif
 		}
 	}