fixes #23454; IndexDefect thrown when destructuring a lent tuple

[ringabout]

fixes #23454

[Araq]

Adhoc solution plus it's unclear to me why var T would not have the same problem.

[ringabout]

Well, var T does have the similar problems

without mitems

block: # bug #23454
  type
    Letter = enum
      A

    LetterPairs = object
      values: seq[(Letter, string)]

  iterator items(list: var LetterPairs): var (Letter, string) =
    for item in list.values:
      yield item

  var instance = LetterPairs(values: @[(A, "foo")])

  for (a, _) in instance:
    case a
    of A: discard

gives expression has no address, I suppose there is a hidden address for var/lent

block: # bug #23454
  type
    Letter = enum
      A

    LetterPairs = object
      values: seq[(Letter, string)]

  iterator items(list: var LetterPairs): var (Letter, string) =
    for item in list.values.mitems:
      yield item

  var instance = LetterPairs(values: @[(A, "foo")])

  for (a, _) in instance:
    case a
    of A: discard

Error: unhandled exception: index 1 not in 0 .. 0 [IndexDefect]

[ringabout]

Succeeded by #23963