Fix scalar dataset with compound dtype for export

[stephprince]

Motivation

This is a follow up to #1176.

The pynwb roundtrip export tests for ElectrodeGroupIO were failing for the scalar compound dataset because on export
options[‘dtype’] was a <class 'numpy.dtype[void]'> and not a list:

hdmf/src/hdmf/backends/hdf5/h5tools.py

Lines 1195 to 1196 in 1abb8ec

	# Write a compound dataset, i.e, a dataset with compound data type
	elif isinstance(options['dtype'], list):

Converting the dtype to a list like the non-scalar compound datatypes fixes this and also allows me to revert some changes I had made in the previous PR to the validator.

How to test the behavior?

Show how to reproduce the new behavior (can be a bug fix or a new feature)

Checklist

• Did you update CHANGELOG.md with your changes?
• Does the PR clearly describe the problem and the solution?
• Have you reviewed our Contributing Guide?
• Does the PR use "Fix #XXX" notation to tell GitHub to close the relevant issue numbered XXX when the PR is merged?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.03%. Comparing base (b5235a7) to head (357e28d).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1185   +/-   ##
=======================================
  Coverage   89.02%   89.03%           
=======================================
  Files          45       45           
  Lines        9879     9883    +4     
  Branches     2812     2813    +1     
=======================================
+ Hits         8795     8799    +4     
  Misses        767      767           
  Partials      317      317           

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[stephprince]

If I understand correctly the failing tests are addressed in #1194, I can wait for that PR to be merged to merge this one.