Ensure calling the BLE connection unsubscribe multiple times does not raise

Adds coverage for this case since we have workarounds in HA that we can
remove since its now safe

tests/test_client.py

@@ -1821,6 +1821,15 @@ async def test_bluetooth_device_connect(
     await asyncio.sleep(0)
     assert states == [(True, 23, 0), (False, 23, 7)]
 
+    # Make sure cancel is safe to call again
+    cancel()
+
+    await client.disconnect(force=True)
+    await asyncio.sleep(0)
+    assert not client._connection
+    # Make sure cancel is safe to call after disconnect
+    cancel()
+
 
 @pytest.mark.asyncio
 async def test_bluetooth_device_connect_and_disconnect_times_out(