patch 8.2.3989: some insert completion code is not tested

Problem:    Some insert completion code is not tested.
Solution:   Add a few tests.  Refactor thesaurus completion. (Yegappan
            Lakshmanan, closes #9460)
diff --git a/src/version.c b/src/version.c
index 21e11dc..6cff7cc 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3989,
+/**/
     3988,
 /**/
     3987,