Adjusted editable_warning for "This resource was imported...." alert:

- fixed a typo from it's to its
- added 'then' to make it clearer

editor/editor_node.cpp

@@ -1454,7 +1454,7 @@ void EditorNode::_edit_current() {
 			}
 		} else if (current_res->get_path().is_resource_file()) {
 			if (FileAccess::exists(current_res->get_path() + ".import")) {
-				editable_warning = TTR("This resource was imported, so it's not editable. Change it's settings in the import panel and re-import.");
+				editable_warning = TTR("This resource was imported, so it's not editable. Change its settings in the import panel and then re-import.");
 			}
 		}
 	} else if (is_node) {