ValueError on BLERadio.start_scan() and ble_detailed_scan.py

I tried running `ble_detailed_scan.py` and get the following error:

```
scanning
Traceback (most recent call last):
File "code.py", line 14, in
File "adafruit_ble/__init__.py", line 250, in start_scan
ValueError: Prefix buffer must be on the heap
```

I _think_ the error happens because the example scans for both services advertisements and any advertisement:

https://github.com/adafruit/Adafruit_CircuitPython_BLE/blob/4eca28e6407f511d5051fd608a238a9d8b40d783/examples/ble_detailed_scan.py#L18

which the causes the prefixes buffer to be empty:

https://github.com/adafruit/Adafruit_CircuitPython_BLE/blob/4eca28e6407f511d5051fd608a238a9d8b40d783/adafruit_ble/__init__.py#L244-L248

That seems to trigger the error here:

https://github.com/adafruit/circuitpython/blob/0dfb7a9a2da1444ebca4b8fff0b88795afede895/shared-bindings/_bleio/Adapter.c#L348-L355

I managed to get the example to work by either removing `Advertisement` from the scan_start() call, or commenting out the prefix check in `_bleio/Adapter.c`.

What I'm not sure about is the relevant code doesn't seem to have changed in the last 1.5 years. I'm using CircuitPython from the latest git commit on the micro:bit v2, so perhaps something weird is happening with my setup. But I thought I would open this issue just in case either something is wrong,.