Fix `BootGodDb.Identify` mutating lookup

fixes f010d6f80, 633216be1

src/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/BootGodDB.cs

@@ -158,7 +158,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 #else
 			if (acquire == null) throw new InvalidOperationException("Bootgod DB not initialized. It's a client responsibility because only a client knows where the database is located.");
 			acquire.WaitOne();
-			return instance._sha1Table.GetValueOrPutNew(sha1);
+			return instance._sha1Table.TryGetValue(sha1, out var l) ? l : new(capacity: 0);
 #endif
 		}
 	}