patch 8.1.0689: undo with text properties not tested

Problem:    Undo with text properties not tested.
Solution:   Add a test function.
diff --git a/src/version.c b/src/version.c
index 3edb146..4b7c9ae 100644
--- a/src/version.c
+++ b/src/version.c
@@ -800,6 +800,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    689,
+/**/
     688,
 /**/
     687,