Using `Nat.lt_trans` is too restrictive, and using `Nat.lt_of_lt_of_le`
should make this tactic prove more goals.
This fixes a regression probably introduced by #3991; at least in some
cases before that `apply sizeOf_get` would have solved the goal here.
And it’s true that this is now subsumed by `simp`, but because of the
order that `macro_rules` are tried, the too restrictive variant with
`Nat.lt_trans` would be tried before `simp`, without backtracking.
Fixes#5027
