[CPyCppyy] Add missing std::string executors

Author: guitargeek

bindings/pyroot/cppyy/CPyCppyy/src/Executors.cxx

@@ -1088,7 +1088,9 @@ struct InitExecFactories_t {
         gf["char16_t*"] =                   (ef_t)+[](cdims_t) { static CString16Executor e{};   return &e;};
         gf["char32_t*"] =                   (ef_t)+[](cdims_t) { static CString32Executor e{};   return &e;};
         gf["std::string"] =                 (ef_t)+[](cdims_t) { static STLStringExecutor e{};   return &e; };
+        gf["string"] =                      gf["std::string"];
         gf["std::string&"] =                (ef_t)+[](cdims_t) { return new STLStringRefExecutor{}; };
+        gf["string&"] =                     gf["std::string&"];
         gf["std::wstring"] =                (ef_t)+[](cdims_t) { static STLWStringExecutor e{};  return &e; };
         gf[WSTRING1] =                      gf["std::wstring"];
         gf[WSTRING2] =                      gf["std::wstring"];