Gui: Remove newline from dialog string

This commit removes superflous newline that disrupts the flow of the sentence displayed in the VarSet dialog. See FreeCAD#16776

src/Gui/DlgAddPropertyVarSet.cpp

@@ -386,9 +386,10 @@ class CreatePropertyException : public std::exception {
 void DlgAddPropertyVarSet::checkName() {
     std::string name = ui->lineEditName->text().toStdString();
     if(name.empty() || name != Base::Tools::getIdentifier(name)) {
-        critical(QObject::tr("Invalid name"),
-                 QObject::tr("The property name must only contain alpha numericals,\n"
-                             "underscore, and must not start with a digit."));
+        QMessageBox::critical(getMainWindow(),
+                              QObject::tr("Invalid name"),
+                              QObject::tr("The property name must only contain alpha numericals, \n"
+                                          "underscore, and must not start with a digit."));
         clearEditors(!CLEAR_NAME);
         throw CreatePropertyException("Invalid name");
     }