patch 8.2.3390: included xdiff code is outdated

Problem:    Included xdiff code is outdated.
Solution:   Sync with xdiff in git 2.33. (Christian Brabandt, closes #8431)
diff --git a/src/version.c b/src/version.c
index fd854d5..ce649e0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3390,
+/**/
     3389,
 /**/
     3388,