spreading_factor = 6 does not work on Ra-02 (SX1278)

I can transmit and receive data if I set the spreading factor anywhere between 7 (default) and 12 on both transmitter and receiver, but setting it to 6 fails to transmit/receive anything.

I'm using Adafruit CircuitPython 9.2.0 on 2024-10-28 on a Waveshare ESP32-S3-Zero with ESP32S3, with a Ra-02 LoRa module (https://www.aliexpress.com/item/32965792976.html)

Start by reproducing the failure with spreading factor 6 on the stated Waveshare ESP32-S3-Zero and Ra-02 hardware, then inspect the library's spreading-factor configuration and radio setup. Done means transmit and receive work at spreading factor 6 while the existing factors 7–12 continue to work.

Written by the indexing model from the issue text.