Fix grind failure in Automata/NA/Sum.lean

Author: ctchou

Cslib/Computability/Automata/NA/Sum.lean

@@ -71,7 +71,9 @@ theorem iSum_language_eq {na : (i : I) → NA (State i) Symbol} {acc : (i : I) 
   constructor
   · rintro ⟨ss, h_run, h_acc⟩
     simp only [mem_iUnion] at h_acc
-    grind
+    #adaptation_note
+    /-- A grind regression found moving to nightly-2026-03-31 (changes from lean#13166) -/
+    grind [Accepts]
   · rintro ⟨i, ss_i, _⟩
     use ss_i.map (Sigma.mk i)
     simp only [mem_iUnion]