patch 8.2.2956: Vim9: need to plan for future additions

Problem:    Vim9: need to plan for future additions.
Solution:   Reserve commands for future use: :type, :class, :enum.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2956,
 /**/
     2955,
 /**/