Fix `load_document_by_uri` method #998

Job	Run time
CI linters via Tox (lint-readme)	23s
cwl-utils release test	5m 28s
CI linters via Tox (pydocstyle)	13s
CI tests via Tox (3, 9, lint)	17s
CI tests via Tox (3, 9, unit)	34s
CI tests via Tox (3, 9, bandit)	26s
CI tests via Tox (3, 9, mypy)	55s
CI tests via Tox (3, 10, lint)	15s
CI tests via Tox (3, 10, unit)	58s
CI tests via Tox (3, 10, bandit)	29s
CI tests via Tox (3, 10, mypy)	44s
CI tests via Tox (3, 11, lint)	16s
CI tests via Tox (3, 11, unit)	56s
CI tests via Tox (3, 11, bandit)	21s
CI tests via Tox (3, 11, mypy)	46s
CI tests via Tox (3, 12, lint)	16s
CI tests via Tox (3, 12, unit)	50s
CI tests via Tox (3, 12, bandit)	23s
CI tests via Tox (3, 12, mypy)	51s
CI tests via Tox (3, 13, lint)	29s
CI tests via Tox (3, 13, unit)	56s
CI tests via Tox (3, 13, bandit)	35s
CI tests via Tox (3, 13, mypy)	57s
	18m 18s

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