Fix/test datasets output

[JulianFlesch]

• Fixes a bug in test-dataset with a broken import that was silent until the CLI speedup refactoring moved rich imports into top-level functions.
• Adds test for test-datasets list
• Catches an error if branch information cannot be fetched.

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

[codecov]

Codecov Report

❌ Patch coverage is 69.23077% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.39%. Comparing base (d91668e) to head (500141e).

Files with missing lines	Patch %	Lines
nf_core/test_datasets/test_datasets_utils.py	25.00%	3 Missing ⚠️
nf_core/test_datasets/list.py	80.00%	1 Missing ⚠️

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