Add test for code that raises pandas warning

[dstansby]

Should fix #72. It looks like the warning is a mistake on pandas part (pandas-dev/pandas#48701) which will be fixed in their next bugfix release, 1.5.1.

[ConorMacBride]

I just ran the tox env py310-sunpy on the pandas git repo and the warning is still shown. I think the issue referenced above is different to the warning? The drms pytest config should be updated to raise all warnings as errors. That way the new test can fail if a warning is presented.

[dstansby]

Woops, my bad. I've had more of a look into this and can't work out how to map the warning

FutureWarning: In a future version, `df.iloc[:, i] = newvals` will attempt to set the values inplace instead of always setting a new array. To retain the old behavior, use either `df[df.columns[i]] = newvals` or, if columns are non-unique, `df.isetitem(i, newvals)`
/home/runner/work/sunpy/sunpy/docs/guide/acquiring_data/jsoc.rst:60: UnexpectedException

to a change in the code, given we're not taking an empty slice as the first argument to iloc.