Add default name="units" to Units object in the mock_Units testing function

[h-mayorquin]

Related to this discussion here:
#1882

This is a quality of life small change that would allow two things to work:

• This part of the code:
  https://github.com/h-mayorquin/pynwb/blob/ad6b0283c49ce8c391fd1b0e6ced3d0f6907c17d/src/pynwb/testing/mock/ecephys.py#L148-L150
• The following script for testing:

from pynwb.testing.mock.file import mock_NWBFile
from pynwb.testing.mock.ecephys import mock_Units

nwbfile = mock_NWBFile()
units_table = mock_Units(num_units=5)
nwbfile.units = units_table

The only downside is that for Units object that are destined for some other places of the nwbfile (.e.g processing) this will not follow the best practices. As these are functions that are mainly used for testing I think that this is not a big deal.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.82%. Comparing base (2259bed) to head (9dcf7f9).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1883      +/-   ##
==========================================
- Coverage   91.81%   83.82%   -8.00%     
==========================================
  Files          27       27              
  Lines        2627     2627              
  Branches      688      688              
==========================================
- Hits         2412     2202     -210     
- Misses        142      330     +188     
- Partials       73       95      +22     

Flag	Coverage Δ
integration	?
unit	83.82% <ø> (ø)

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[rly]

Looks good. Thanks @h-mayorquin