Bump virtualenv from 20.2.2 to 20.4.3 in /requirements

[dependabot]

Bumps virtualenv from 20.2.2 to 20.4.3.

Changelog

Sourced from virtualenv's changelog.

v20.4.3 (2021-03-16)

Bugfixes - 20.4.3

- Bump embeded setuptools from ``52.0.0`` to ``54.1.2`` - by :user:`gaborbernat` (`[#2069](https://github.com/pypa/virtualenv/issues/2069) <https://github.com/pypa/virtualenv/issues/2069>`_)
- Fix PyPy3 stdlib on Windows is incorrect - by :user:`gaborbernat`. (`[#2071](https://github.com/pypa/virtualenv/issues/2071) <https://github.com/pypa/virtualenv/issues/2071>`_)
v20.4.2 (2021-02-01)
Bugfixes - 20.4.2

• Running virtualenv --upgrade-embed-wheels crashes - by :user:gaborbernat. ([#2058](https://github.com/pypa/virtualenv/issues/2058) <https://github.com/pypa/virtualenv/issues/2058>_)

v20.4.1 (2021-01-31)

Bugfixes - 20.4.1

- Bump embedded pip and setuptools packages to latest upstream supported (``21.0.1`` and ``52.0.0``) - by :user:`gaborbernat`. (`[#2060](https://github.com/pypa/virtualenv/issues/2060) <https://github.com/pypa/virtualenv/issues/2060>`_)
v20.4.0 (2021-01-19)
Features - 20.4.0

• On the programmatic API allow passing in the environment variable dictionary to use, defaults to os.environ if not specified - by :user:gaborbernat. ([#2054](https://github.com/pypa/virtualenv/issues/2054) <https://github.com/pypa/virtualenv/issues/2054>_)

Bugfixes - 20.4.0

- Upgrade embedded setuptools to ``51.3.3`` from ``51.1.2`` - by :user:`gaborbernat`. (`[#2055](https://github.com/pypa/virtualenv/issues/2055) <https://github.com/pypa/virtualenv/issues/2055>`_)
v20.3.1 (2021-01-13)
Bugfixes - 20.3.1

• Bump embed pip to 20.3.3, setuptools to 51.1.1 and wheel to 0.36.2 - by :user:gaborbernat. ([#2036](https://github.com/pypa/virtualenv/issues/2036) <https://github.com/pypa/virtualenv/issues/2036>_)
• Allow unfunctioning of pydoc to fail freely so that virtualenvs can be activated under Zsh with set -e (since otherwise unset -f and unfunction exit with 1 if the function does not exist in Zsh) - by :user:d125q. ([#2049](https://github.com/pypa/virtualenv/issues/2049) <https://github.com/pypa/virtualenv/issues/2049>_)
• Drop cached python information if the system executable is no longer present (for example when the executable is a shim and the mapped executable is replaced - such is the case with pyenv) - by :user:gaborbernat. ([#2050](https://github.com/pypa/virtualenv/issues/2050) <https://github.com/pypa/virtualenv/issues/2050>_)

... (truncated)

Commits

• 39911d5 release 20.4.3
• ce24cb5 Bump setuptools to 54.1.2
• 31fcce5 [pre-commit.ci] pre-commit autoupdate (#2077)
• 71f96cd Fix PyPy3 Windows stlib path (#2072)
• 742e145 [pre-commit.ci] pre-commit autoupdate (#2075)
• 3d03091 [pre-commit.ci] pre-commit autoupdate (#2064)
• a89bc0e fix typos in user guide (#2070)
• 4740930 Upgrade setuptools (#2069)
• 957e838 Merge pull request #2063 from pypa/release-20.4.2
• 325e95e release 20.4.2
• Additional commits viewable in compare view

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[dependabot]

Looks like virtualenv is no longer a dependency, so this is no longer needed.