Fix tree title column size minimum width

scene/gui/tree.cpp

@@ -4043,7 +4043,7 @@ int Tree::get_column_minimum_width(int p_column) const {
 
 	// Check if the visible title of the column is wider.
 	if (show_column_titles) {
-		min_width = MAX(cache.font->get_string_size(columns[p_column].title).width, min_width);
+		min_width = MAX(cache.font->get_string_size(columns[p_column].title).width + cache.bg->get_margin(SIDE_LEFT) + cache.bg->get_margin(SIDE_RIGHT), min_width);
 	}
 
 	if (!columns[p_column].clip_content) {