Fix flat.v which broke for some reason

Also update IRIS_VERSION because I can't be bothered to downgrade now...

IRIS_VERSION

-bb5e21f21fd1b5be820005eb53750f84270ab4ec
+05a588df59ddfdc2e7a4aec5a98a50614c819693

_CoqProject

 -Q . iris_atomic
--Q iris iris
 atomic.v
 sync.v
 atomic_incr.v

flat.v

@@ -305,9 +305,9 @@ Section proof.
     iIntros (?) "(#? & #? & #? & HΦ)".
     wp_seq. wp_let.
     wp_bind (try_acquire _). iApply try_acquire_spec.
-    iFrame "#". iSplit; last by wp_if.
+    iFrame "#". iNext. iIntros ([]); last by (iIntros; wp_if).
     (* acquired the lock *)
-    iIntros "Hlocked [Ho2 HR]".
+    iIntros "[Hlocked [Ho2 HR]]".
     wp_if. wp_bind (! _)%E.
     iInv N as "[H >Hm]" "Hclose".
     iDestruct "H" as (xs' hd') "[>Hs [>Hxs HRs]]".