patch 8.2.3839: using \z() with \z1 not tested for syntax highlighting

Problem:    Using \z() with \z1 not tested for syntax highlighting.
Solution:   Add a test. (Dominique Pellé, closes #9365)
diff --git a/src/version.c b/src/version.c
index eb09d61..be0122d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3839,
+/**/
     3838,
 /**/
     3837,