Add rename_extends test

Author: adamscott

modules/gdscript/tests/scripts/refactor/rename/tests/type/rename_extends.cfg

@@ -0,0 +1,12 @@
+; This test renames (at least, tries to rename) `extends`.
+[input]
+refactor={
+	"file": "res://scripts/class_a.gd",
+	"line": 1,
+	"column": 1,
+	"symbol": "extends",
+}
+[output]
+outside_refactor = true
+refactor_has_failed = true
+refactor_result_type = "KEYWORD"