Bump tox from 3.7.0 to 3.21.2

[dependabot-preview]

Bumps tox from 3.7.0 to 3.21.2.

Changelog

Sourced from tox's changelog.

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
• Fix platform support for install_command. - by jayvdb #1464
• Fixed regression in v3.20.0 that caused escaped curly braces in setenv to break usage of the variable elsewhere in tox.ini. - by jayvdb #1690
• Prevent {} and require {: is only followed by }. - by jayvdb #1711
• Raise MissingSubstitution on access of broken ini setting. - by jayvdb #1716

Features

• Allow { and } in default of {env:key:default}. - by jayvdb #1502
• Allow {posargs} in setenv. - by jayvdb #1695
• Allow {/} to refer to os.sep. - by jayvdb #1700
• Make parsing [testenv] sections in setup.cfg official. - by mauvilsa #1727
• Relax importlib requirement to allow 3.0.0 or any newer version - by pkolbus #1763

Documentation

... (truncated)

Commits

• 4116e90 release 3.21.2
• 1d23293 Newer coverage plugin updates env-vars, ignore in pytest plugin (#1854)
• 6624a8c Add missing backticks to my username (#1851)
• 51cd5fd Update README.md
• cc26279 Merge pull request #1808 from tox-dev/release-3.21.1
• ffac605 release 3.21.1
• 4b44584 config: Prevent .tox in envlist
• ff4bd47 config: Revert removal of {packages}/{opts} hack
• c1c1c5b test_config: Add test for indirect install_command
• 3914667 Allow building with setuptools_scm 4 and 5
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #583.