Update dependency yamllint to v1.26.3

This MR contains the following updates:

Package	Type	Update	Change
yamllint	ironbank-pypi	minor	1.25.0 -> 1.26.3

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Release Notes

adrienverge/yamllint

v1.26.3

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• Restore runtime dependency setuptools for Python < 3.8

v1.26.2

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• Fix python_requires to comply with PEP 345 and PEP 440

v1.26.1

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• Remove runtime dependency setuptools for Python < 3.8
• Fix line_length to skip all hash signs starting comment

v1.26.0

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• End support for Python 2 and Python 3.4, add support for Python 3.9
• Add forbid: non-empty option to braces and brackets rules
• Fix quoted-strings for explicit octal recognition
• Add documentation for integration with Arcanist
• Fix typos in changelog and README
• Stop using deprecated python setup.py test in tests

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