Fix RetroAchievements dev search freezes

Re-added a line of code from a cancelled PR (that I thought was in
main already) that RetroAchievements uses to properly synchronize
memory reads and writes with the emulator frames. This appears to
fix some pretty major freezing and deadlocks in the RA dev tools.

Source/Core/Core/AchievementManager.cpp

@@ -1503,6 +1503,7 @@ void AchievementManager::LoadIntegrationCallback(int result, const char* error_m
   case RC_OK:
     INFO_LOG_FMT(ACHIEVEMENTS, "RAIntegration.dll found.");
     instance.m_dll_found = true;
+    rc_client_set_allow_background_memory_reads(instance.m_client, 0);
     rc_client_raintegration_set_event_handler(instance.m_client, RAIntegrationEventHandler);
     rc_client_raintegration_set_write_memory_function(instance.m_client, MemoryPoker);
     rc_client_raintegration_set_get_game_name_function(instance.m_client, GameTitleEstimateHandler);