[Python][Parquet][Emscripten] PARQUET_TEST_DATA isn't set in test-conda-python-emscripten

[kou]

Describe the bug, including details regarding any error messages, version, and platform.

It's required since #41580.

https://github.com/ursacomputing/crossbow/actions/runs/10604493737/job/29391275377#step:7:8847

 ==================================== ERRORS ====================================
____________ ERROR at setup of test_column_chunk_key_value_metadata ____________

    @pytest.fixture(scope='module')
    def parquet_test_datadir():
        result = os.environ.get('PARQUET_TEST_DATA')
        if not result:
>           raise RuntimeError('Please point the PARQUET_TEST_DATA environment '
                               'variable to the test data directory')
E           RuntimeError: Please point the PARQUET_TEST_DATA environment variable to the test data directory

/lib/python3.12/site-packages/pyarrow/tests/parquet/conftest.py:35: RuntimeError

Component(s)

Parquet, Python

[kou]

Issue resolved by pull request 43906
#43906