Fix firmware flash button not disabled while connecting

We were using the wrong state variable to detect when BLE is disconnected.
We care about the BLE connection state, not the hub runtime state here.

Issue: https://github.com/pybricks/support/issues/315#issuecomment-841486591

src/firmware/FlashButton.tsx

@@ -2,7 +2,7 @@
 // Copyright (c) 2020-2021 The Pybricks Authors
 
 import { connect } from 'react-redux';
-import { HubRuntimeState } from '../hub/reducers';
+import { BleConnectionState } from '../ble/reducers';
 import { BootloaderConnectionState } from '../lwp3-bootloader/reducers';
 import * as notification from '../notifications/actions';
 import { RootState } from '../reducers';
@@ -22,7 +22,7 @@ const mapStateToProps = (state: RootState): StateProps => ({
     tooltip: state.firmware.flashing ? TooltipId.FlashProgress : TooltipId.Flash,
     enabled:
         state.bootloader.connection === BootloaderConnectionState.Disconnected &&
-        state.hub.runtime === HubRuntimeState.Disconnected,
+        state.ble.connection === BleConnectionState.Disconnected,
     showProgress: state.firmware.flashing,
     progress: state.firmware.progress === null ? undefined : state.firmware.progress,
 });