Add missing BurnTx type to Auth.tx fcode table

init_type_env/0 listed five new Chain.base_tx constructors in
con_env and arities but omitted BurnTx from the variant type,
so compiling switches on Chain.BurnTx crashed in split_vars/2.

src/so_ast_to_fcode.erl

@@ -335,7 +335,8 @@ init_type_env() ->
                         [address, integer],
                         [integer],
                         [{list, {tuple, [{variant, [[], [address]]}, address, address, integer]}}],
-                        [address, integer, string, {list, {tuple, [address, integer]}}]
+                        [address, integer, string, {list, {tuple, [address, integer]}}],
+                        [integer]
                        ]},
     #{ ["int"]             => ?type(integer),
        ["bool"]            => ?type(boolean),