App: modernize C++: return braced init list

src/App/GeoFeatureGroupExtensionPyImp.cpp

@@ -33,10 +33,9 @@ using namespace App;
 // returns a string which represents the object e.g. when printed in python
 std::string GeoFeatureGroupExtensionPy::representation() const
 {
-    return std::string("<GeoFeatureGroup object>");
+    return {"<GeoFeatureGroup object>"};
 }
 
-
 PyObject *GeoFeatureGroupExtensionPy::getCustomAttributes(const char* /*attr*/) const
 {
     return nullptr;