patch 8.2.3226: new digraph functions use old naming scheme

Problem:    New digraph functions use old naming scheme.
Solution:   Use the digraph_ prefix. (Hirohito Higashi, closes #8580)
diff --git a/src/version.c b/src/version.c
index 945d8e9..0d60cc2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3226,
+/**/
     3225,
 /**/
     3224,