convs are ignored for var tuples in transf

[ringabout]

          Smaller case:

type A = object
  field: tuple[a: int]

func value(v: var A): var tuple[a: int] =
  v.field
template get(v: A): tuple[a: int] = v.value

var v = A(field: (a: 1))
echo get(v)[0]

error: 'T2_' is a pointer; did you mean to use '->'?
  T1_[0] = dollar___systemZdollars_u8(T2_.Field0);
                                         ^
                                         ->

Originally posted by @metagn in #22049 (comment)