Bump tox from 3.20.1 to 3.21.4 in /ngraph/python

[dependabot]

Bumps tox from 3.20.1 to 3.21.4.

Changelog

Sourced from tox's changelog.

v3.21.4 (2021-02-02)

Bugfixes ^^^^^^^^

• Adapt tests not to assume the easy_install command exists, as it was removed from setuptools 52.0.0+ - by :user:hroncok [#1893](https://github.com/tox-dev/tox/issues/1893) <https://github.com/tox-dev/tox/issues/1893>_

v3.21.3 (2021-01-28)

Bugfixes ^^^^^^^^

• Fix a killed tox (via SIGTERM) leaving the commands subprocesses running by handling it as if it were a KeyboardInterrupt - by :user:dajose [#1772](https://github.com/tox-dev/tox/issues/1772) <https://github.com/tox-dev/tox/issues/1772>_

v3.21.2 (2021-01-19)

Bugfixes ^^^^^^^^

• Newer coverage tools update the COV_CORE_CONTEXT environment variable, add it to the list of environment variables that can change in our pytest plugin - by :user:gaborbernat. [#1854](https://github.com/tox-dev/tox/issues/1854) <https://github.com/tox-dev/tox/issues/1854>_

v3.21.1 (2021-01-13)

Bugfixes ^^^^^^^^

• Fix regression that broke using install_command in config replacements - by :user:jayvdb [#1777](https://github.com/tox-dev/tox/issues/1777) <https://github.com/tox-dev/tox/issues/1777>_
• Fix regression parsing posargs default containing colon. - by :user:jayvdb [#1785](https://github.com/tox-dev/tox/issues/1785) <https://github.com/tox-dev/tox/issues/1785>_

Features ^^^^^^^^

• Prevent .tox in envlist - by :user:jayvdb [#1684](https://github.com/tox-dev/tox/issues/1684) <https://github.com/tox-dev/tox/issues/1684>_

... (truncated)

Commits

• ff9990a release 3.21.4
• 7355b65 Adapt tests not to assume easy_install exists, it was removed from setuptools...
• a42ff11 Merge pull request #1880 from tox-dev/release-3.21.3
• 7dbed25 release 3.21.3
• 15533dd [pre-commit.ci] pre-commit autoupdate (#1872)
• 8a2bb56 Format markdown
• 6725807 tox use discord
• 833b33f Handle sigterm by killing the commands subprocess (#1860)
• 3d80588 Merge pull request #1858 from tox-dev/release-3.21.2
• 4116e90 release 3.21.2
• Additional commits viewable in compare view

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[dependabot]

Dependabot tried to add @postrational as a reviewer to this PR, but received the following error from GitHub:

POST https://api.github.com/repos/tomdol/openvino/pulls/9/requested_reviewers: 422 - Reviews may only be requested from collaborators. One or more of the users or teams you specified is not a collaborator of the tomdol/openvino repository. // See: https://docs.github.com/rest/reference/pulls#request-reviewers-for-a-pull-request

[dependabot]

The following labels could not be found: category: dependencies.