Fix log issue when importing celeba and align celeba dataset

[sooahleex]

Summary

When import celeba or align_celeba dataset without format like dm.Dataset.import_from(path=...), we met error like below. The example is the case for importing align_celeba dataset.

ERROR:root:Cannot find celeba's images directory at tests/assets/align_celeba_dataset/dataset/Img/img_celeba

How to test

Checklist

• I have added unit tests to cover my changes.​
• I have added integration tests to cover my changes.​
• I have added the description of my changes into CHANGELOG.​
• I have updated the documentation accordingly

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below).

# Copyright (C) 2023 Intel Corporation
#
# SPDX-License-Identifier: MIT

[codecov-commenter]

Codecov Report

Patch coverage: 83.33% and project coverage change: -2.85 ⚠️

Comparison is base (89b2111) 78.87% compared to head (e423085) 76.02%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #919      +/-   ##
===========================================
- Coverage    78.87%   76.02%   -2.85%     
===========================================
  Files          210      231      +21     
  Lines        25145    26508    +1363     
  Branches      5036     5298     +262     
===========================================
+ Hits         19832    20153     +321     
- Misses        4178     5195    +1017     
- Partials      1135     1160      +25     

Flag	Coverage Δ
macos-11_Python-3.8	75.06% <83.33%> (-2.80%)	⬇️
ubuntu-20.04_Python-3.8	76.01% <83.33%> (-2.85%)	⬇️
windows-2019_Python-3.8	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
datumaro/plugins/data_formats/celeba/celeba.py	74.05% <83.33%> (+0.63%)	⬆️

... and 30 files with indirect coverage changes

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[vinnamkim]

LGTM.