Fix inherited readonly props

[ehennestad]

Motivation

Some schema attributes are redefined to be readonly for inherited classes. In MATLAB a property attribute can not be redefined for subclasses, so it was possible to set readonly properties.

How to test the behavior?

es = types.core.ElectricalSeries()
es.data_unit = 'volt' % works
es.data_unit = 'millivolts' % should not work

Checklist

• [x] Have you ensured the PR description clearly describes the problem and solutions?
• [x] Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• [ ] If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?

[lawrence-mbf]

@ehennestad This is not kosher but could you apply the fix mentioned in here: https://github.com/NeurodataWithoutBorders/matnwb/issues/262#issuecomment-1923619681 as most of the errors in these tests come from there.

[ehennestad]

The failed test is actually a good sign!

Error using types.core/ElectricalSeries/validate_data_unit
Unable to set the 'data_unit' property of class '<a href="matlab:doc
types.core.ElectricalSeries">ElectricalSeries</a>' because it is read-only.

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (9d77234) 88.49% compared to head (d8d18f0) 88.52%.

Files	Patch %	Lines
+file/fillValidators.m	95.83%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #560 +/- ## ========================================== + Coverage 88.49% 88.52% +0.02% ========================================== Files 104 104 Lines 4616 4636 +20 ========================================== + Hits 4085 4104 +19 - Misses 531 532 +1 ```

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