Bump pip from 21.3 to 21.3.1 (#438)

Bumps [pip](https://github.com/pypa/pip) from 21.3 to 21.3.1.
- [Release notes](https://github.com/pypa/pip/releases)
- [Changelog](https://github.com/pypa/pip/blob/main/NEWS.rst)
- [Commits](https://github.com/pypa/pip/compare/21.3...21.3.1

)

---
updated-dependencies:
- dependency-name: pip
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.build.txt

-pip==21.3
+pip==21.3.1