Tempest job fails to install reno

Uploaded a review in Swift and this happens in Tempest:

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Collecting unittest2>=1.1.0
  Using cached https://mirror.mtl01.iweb.opendev.org/wheel/ubuntu-20.04-x86_64/unittest2/unittest2-1.1.0-py2.py3-none-any.whl (96 kB)
Collecting openstackdocstheme>=2.2.0
  Downloading https://mirror.mtl01.iweb.opendev.org/pypifiles/packages/da/88/0c2a4b6f728b242351d8929c9dc6d4e41eec2f01514ad616e87a92c6992f/openstackdocstheme-2.3.0-py3-none-any.whl (1.1 MB)
/opt/stack/tempest/.tox/venv/lib/python3.8/site-packages/pip/_vendor/packaging/version.py:111: DeprecationWarning: Creating a LegacyVersion has been deprecated and will be removed in the next major release
  warnings.warn(
ERROR: Cannot install reno>=3.1.0 because these package versions have conflicting dependencies.

The conflict is caused by:
    The user requested reno>=3.1.0
    The user requested (constraint) reno===3.4.0

To fix this you could try to:
1. loosen the range of package versions you've specified
2. remove package versions to allow pip attempt to solve the dependency conflict

ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/user_guide/#fixing-conflicting-dependencies
WARNING: You are using pip version 21.2.3; however, version 21.2.4 is available.
You should consider upgrading via the '/opt/stack/tempest/.tox/venv/bin/python -m pip install --upgrade pip' command.
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No idea what this is about, I think Swift does not use reno at all.
It used to be needed for py2, but not anymore.

Review URL:
 https://review.opendev.org/c/openstack/swift/+/787656