This was fixed for v100. Once DietPi runs the update and reboots, the issue should disappear.
If the issue re-occurs after v100. Try running the following:
/DietPi/dietpi/dietpi-apt-get_update 2
apt-get install iw crda --no-install-recommends -y
If that doesnt fix it, you may need to manually enter your country code in /etc/default/crda (resolved) calling CRDA many times and failing on boot. - #4 by Gord_W