Adicionar teste para AffiliationsListValidation.validate_affiliation_count_article_vs_sub_article

[robertatakenaka]

• o que acontece se há mais de 1 sub-article do tipo translation?
• tests/samples/1518-8787-rsp-56-79.xml: No such file or directory

ERROR: test_validate_affiliation_count_article_vs_sub_article (tests.sps.validation.test_aff.AffiliationValidationTest)
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Traceback (most recent call last):
  File "/Users/roberta.takenaka/github.com/scieloorg/packtools/packtools/tests/sps/validation/test_aff.py", line 648, in test_validate_affiliation_count_article_vs_sub_article
    xml_tree = xml_utils.get_xml_tree("tests/samples/1518-8787-rsp-56-79.xml")
  File "/Users/roberta.takenaka/github.com/scieloorg/packtools/packtools/packtools/sps/utils/xml_utils.py", line 121, in get_xml_tree
    raise exceptions.SPSLoadToXMLError(str(exc)) from None
packtools.sps.exceptions.SPSLoadToXMLError: Start tag expected, '<' not found, line 1, column 1 (<string>, line 1)