Fix bug when exporting HDF5 datasets with unlimited dimension

[oruebel]

Motivation

Fix #154

When an HDF5 file contains datasets with unlimited dimensions, use of the hdmf.utils.get_data_shape method yields the wrong data shape because the functions looks at maxshape first. This leads to an error on export because Zarr cannot create a dataset with undefined dimensions.

How to test the behavior?

See #154

Checklist

• [x] Did you update CHANGELOG.md with your changes?
• [X] Have you checked our Contributing document?
• [X] Have you ensured the PR clearly describes the problem and the solution?
• [X] Is your contribution compliant with our coding style? This can be checked running ruff from the source directory.
• [X] Have you checked to ensure that there aren't other open Pull Requests for the same change?
• [X] Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov-commenter]

Codecov Report

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

Comparison is base (71bfa6d) 85.07% compared to head (21d5a6d) 85.16%.

Files	Patch %	Lines
src/hdmf_zarr/backend.py	75.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #155 +/- ## ========================================== + Coverage 85.07% 85.16% +0.08% ========================================== Files 5 5 Lines 1146 1146 Branches 311 311 ========================================== + Hits 975 976 +1 + Misses 115 114 -1 Partials 56 56 ```

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