patch 8.2.2878: Vim9: for loop list unpack only allows for one "_"

Problem:    Vim9: for loop list unpack only allows for one "_".
Solution:   Drop the value when the variable is "_". (closes #8232)
diff --git a/src/version.c b/src/version.c
index 82ecd0a..0223ae2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2878,
+/**/
     2877,
 /**/
     2876,