patch 8.1.1252: not all mapping completion is tested

Problem:    Not all mapping completion is tested.
Solution:   Add a few more mapping completion tests.
diff --git a/src/version.c b/src/version.c
index 13b35d5..aa0d1e6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1252,
+/**/
     1251,
 /**/
     1250,