Make `iNext` smarter for mixed `▷` and `▷^n`
See below:
From iris Require Import proofmode.tactics.
Lemma foo {M} (P : uPred M) n : ▷ ▷^n P ⊢ ▷^n ▷ P.
Proof. iIntros "H". iNext.
(* Gives
"H" : ▷ ▷^n P
--------------------------------------∗
▷ P
*)