test_attempt_read_encrypted_no_password_xls failure in Python 3.7+

[StevenMaude]

This line specifies an error message. In the test, the text of the exception caused by the code under test is expected to match exactly.

errmsg = "Can't read Excel file: XLRDError('Workbook is encrypted',)"

When running tests on Python 3.7 and 3.8 this fails, because their outputs do not contain the comma (probably due to this change in Python 3.7, I'm guessing).