build(deps): update pip requirement in /.github/workflows (#107)

Updates the requirements on [pip](https://github.com/pypa/pip) to permit the latest version.
- [Release notes](https://github.com/pypa/pip/releases)
- [Changelog](https://github.com/pypa/pip/blob/main/NEWS.rst)
- [Commits](pypa/pip@0.3...21.2.1)

---
updated-dependencies:
- dependency-name: pip
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

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

Author: dependabot[bot]

.github/workflows/constraints.txt

@@ -1,4 +1,4 @@
-pip<21.2
+pip<21.3
 pre-commit==2.13.0
 black==21.7b0
 flake8==3.9.2