Bump pip from 19.0.1 to 21.1.2

[dependabot-preview]

Bumps pip from 19.0.1 to 21.1.2.

Changelog

Sourced from pip's changelog.

21.1.2 (2021-05-23)

Bug Fixes

• New resolver: Correctly exclude an already installed package if its version is known to be incompatible to stop the dependency resolution process with a clear error message. (#9841)
• Allow ZIP to archive files with timestamps earlier than 1980. (#9910)
• Emit clearer error message when a project root does not contain either pyproject.toml, setup.py or setup.cfg. (#9944)
• Fix detection of existing standalone pip instance for PEP 517 builds. (#9953)

21.1.1 (2021-04-30)

Deprecations and Removals

• Temporarily set the new "Value for ... does not match" location warnings level to DEBUG, to hide them from casual users. This prepares pip 21.1 for CPython inclusion, while pip maintainers digest the first intake of location mismatch issues for the distutils-sysconfig transition. (#9912)

Bug Fixes

• This change fixes a bug on Python <=3.6.1 with a Typing feature added in 3.6.2 (#9831)
• Fix compatibility between distutils and sysconfig when the project name is unknown outside of a virtual environment. (#9838)
• Fix Python 3.6 compatibility when a PEP 517 build requirement itself needs to be built in an isolated environment. (#9878)

21.1 (2021-04-24)

Process

• Start installation scheme migration from distutils to sysconfig. A warning is implemented to detect differences between the two implementations to encourage user reports, so we can avoid breakages before they happen.

Features

• Add the ability for the new resolver to process URL constraints. (#8253)
• Add a feature --use-feature=in-tree-build to build local projects in-place when installing. This is expected to become the default behavior in pip 21.3; see Installing from local packages for more information. (#9091)
• Bring back the "(from versions: ...)" message, that was shown on resolution failures. (#9139)
• Add support for editable installs for project with only setup.cfg files. (#9547)
• Improve performance when picking the best file from indexes during pip install. (#9748)
• Warn instead of erroring out when doing a PEP 517 build in presence of --build-option. Warn when doing a PEP 517 build in presence of --global-option. (#9774)

Bug Fixes

• Fixed --target to work with --editable installs. (#4390)
• Add a warning, discouraging the usage of pip as root, outside a virtual environment. (#6409)
• Ignore .dist-info directories if the stem is not a valid Python distribution name, so they don't show up in e.g. pip freeze. (#7269)

... (truncated)

Commits

• 8737f90 Bump for release
• d7cf6ca Update AUTHORS.txt
• 30faa64 Fix duplicate top line in NEWS.rst
• 128ec36 Test case for backtracking an installed candidate
• 729c626 Exclude a known incompatible installed candidate
• 1c31d33 Update src/pip/_internal/build_env.py
• e266aa5 Update news/9910.bugfix.rst
• 00003d5 9910 news
• d55e02c Set strict_timestamps=False when zip is called for isolated environment
• 4f983c4 Handle standalone pip creation from pip wheel
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #612.