patch 8.2.1356: Vim9: cannot get the percent register

Problem:    Vim9: cannot get the percent register.
Solution:   Check for readable registers instead of writable. (closes #6566)

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1356,
 /**/
     1355,
 /**/