Bump tox from 3.7.0 to 3.21.4

[dependabot-preview]

Bumps tox from 3.7.0 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 hroncok #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 dajose #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 gaborbernat. #1854

v3.21.1 (2021-01-13)

Bugfixes

• Fix regression that broke using install_command in config replacements - by jayvdb #1777
• Fix regression parsing posargs default containing colon. - by jayvdb #1785

Features

• Prevent .tox in envlist - by jayvdb #1684

Miscellaneous

• Enable building tox with setuptools_scm 4 and 5 by hroncok #1799

v3.21.0 (2021-01-08)

Bugfixes

• Fix the false congratulations message that appears when a KeyboardInterrupt occurs during package installation. - by gnikonorov #1453

... (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-preview]

Superseded by #588.