test: test_revocation_mode_soft failing due to expired cert

[fanquake]

Similar to the issue fixed in fc82b79, the revocation_mode tests are once again failing:

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ERROR: test_revocation_mode_soft (tests.test_validate.ValidateTests)
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Traceback (most recent call last):
  File "/Users/michael/certvalidator/tests/test_validate.py", line 85, in test_revocation_mode_soft
    validate_path(context, path)
  File "/Users/michael/certvalidator/tests/../certvalidator/validate.py", line 50, in validate_path
    return _validate_path(validation_context, path)
  File "/Users/michael/certvalidator/tests/../certvalidator/validate.py", line 358, in _validate_path
    raise PathValidationError(pretty_message(
certvalidator.errors.PathValidationError: The path could not be validated because the end-entity certificate expired 2022-07-27 12:00:00Z