Update for bt to radiance variable transform change.

[mikecooke77]

Description

The RadToBT_obs_2021071200.nc4 used in the ctest has had the sensorCentralWavelength changed from [Location, Channel] to [Channel]. This tests the functionality of reading in the spectral variable which is just of size Channel.

Dependencies

To be merged with:

• [ ] https://github.com/JCSDA-internal/ufo/pull/3014

Impact

None outside of ufo and ufo-data.

Checklist

• [x] I have performed a self-review of my own code
• [x] I have run the unit tests before creating the PR