ROVER Unhealthy AHRS with CUAV-NORA when running No Gps with Wheel Odometry

## Bug report
This may be complementary to
https://github.com/ArduPilot/ardupilot/issues/7417

**Issue details**
I am running without GPS and just on wheel encoders, I constantly receive "Unhealthy AHRS" message , is there an easy fix ?

**Version**
rover 4.1.1

**Airframe type**
ROVER Differential Drive - aka “Skid steering”

**Hardware type**
CUAV-NORA

**Logs**
[2 12-31-1979 7-00-00 PM.zip](https://github.com/ArduPilot/ardupilot/files/7692311/2.12-31-1979.7-00-00.PM.zip)

Start by reviewing the linked issue #7417 and the attached log for the Rover 4.1.1 setup using CUAV-NORA, differential drive, no GPS, and wheel encoders. Determine why the AHRS is reported unhealthy in this configuration, then validate the resolved behavior against the supplied log scenario.

Written by the indexing model from the issue text.