Add BGS to cell 56 and 70 in minitest

[londumas]

In minitest it would be useful to have the cell 56 and 70 for BGS also:
https://github.com/desihub/desitest/blob/master/mini/minitest.ipynb

[sbailey]

Slightly more context: this is the plot in cell 70 that @londumas is requesting to have BGS included too:

Cell 56 is a plot of similar information, but generated by the minitest notebook itself so doesn't require any desisim QA code updates.

[sbailey]

Cell 56 has been updated to include BGS in the latest notebook run:

Would still be nice to have the deltav vs. z plots updated too to include BGS since that highlights more subtle biases and trends.