patch 8.2.2991: Vim9: no completion for :vim9 and :legacy

Problem:    Vim9: no completion for :vim9 and :legacy.
Solution:   Expand argument as a command. (closes #8377)
diff --git a/src/version.c b/src/version.c
index dfe1f8b..07c775b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2991,
+/**/
     2990,
 /**/
     2989,