bpo-43993: Update vendored pip to 21.1.1

[sbidoul]

https://bugs.python.org/issue43993

[pfmoore]

@ambv@pablogsal Is this OK to go into 3.8/3.9/3.10b1? I'm aware it's pretty close to the release, but typically ensurepip changes are low-impact, and 21.1 contained some rather annoying warnings that we'd like to suppress in the version that gets released with CPython.

[pablogsal]

@ambv@pablogsal Is this OK to go into 3.8/3.9/3.10b1?

LGTM for 3.10b1 but it needs to be merged before Monday to be included

[pfmoore]

Thanks @pablogsal I'll merge now. I won't trigger backports until I have the OK from @ambv though.

[ambv]

OK for both 3.8 and 3.9, please merge ASAP.

[miss-islington]

Thanks @sbidoul for the PR, and @pfmoore for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖

[miss-islington]

Thanks @sbidoul for the PR, and @pfmoore for merging it 🌮🎉.. I'm working now to backport this PR to: 3.8.
🐍🍒⛏🤖

[miss-islington]

Sorry, @sbidoul and @pfmoore, I could not cleanly backport this to 3.9 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker bf99b7151663905fd5e71efe45184dc8fffc3236 3.9

[miss-islington]

Sorry @sbidoul and @pfmoore, I had trouble checking out the 3.8 backport branch.
Please backport using cherry_picker on command line.
cherry_picker bf99b7151663905fd5e71efe45184dc8fffc3236 3.8

[bedevere-bot]

GH-25782 is a backport of this pull request to the 3.9 branch.

[bedevere-bot]

GH-25783 is a backport of this pull request to the 3.8 branch.

[pfmoore]

Thanks @ambv both merges done.