[tox] Use a revision on proper branch for Yams
"default" is not good when some bug fix release suddenly comes out...
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Changelog history
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.. include:: 3.22.rst
.. include:: 3.21.rst
.. include:: 3.20.rst
.. include:: 3.19.rst
.. include:: 3.18.rst
.. include:: 3.17.rst
.. include:: 3.16.rst
.. include:: 3.15.rst
.. include:: 3.14.rst