[chore] Remove Python 3.7 support (backport #5844)

[mergify]

Description

This is an automatic backport of pull request #5844 done by Mergify.

Cherry-pick of 13f87e7 has failed:

On branch mergify/bp/2021/pr-5844
Your branch is up to date with 'origin/2021'.

You are currently cherry-picking commit 13f87e76.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .github/workflows/tests.yml
	modified:   docs/source/getting_started.md
	modified:   pyproject.toml
	modified:   tox.ini
	modified:   wrapper/pyproject.toml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   README-zh-cn.md
	both modified:   README.md

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[mergify]

Cherry-pick of 13f87e7 has failed:

On branch mergify/bp/2021/pr-5844
Your branch is up to date with 'origin/2021'.

You are currently cherry-picking commit 13f87e76.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .github/workflows/tests.yml
	modified:   docs/source/getting_started.md
	modified:   pyproject.toml
	modified:   tox.ini
	modified:   wrapper/pyproject.toml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   README-zh-cn.md
	both modified:   README.md

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[github-actions]

Hi @mergify[bot], I have deleted the conflicted deleted files in this pull request. Please check it again. Thanks!