Fix sizeof test for kaitai-io/kaitai_struct_compiler#236

Author: Mingun

formats_err/expr_sizeof_value_dynamic3.ksy

@@ -1,14 +1,16 @@
-# ?
+# expr_sizeof_value_dynamic3.ksy: /instances/body_sizeof/value:
+# 	error: unable to derive sizeof of `Name(identifier(body))`: dynamic sized type
+#
 meta:
   id: expr_sizeof_value_dynamic3
   endian: le
 seq:
-  - id: num
+  - id: num_body
     type: u2
   - id: body
     type: u1
     repeat: expr
-    repeat-expr: num
+    repeat-expr: num_body
 instances:
   body_sizeof:
     value: body._sizeof