Update pygithub requirement from ~=1.57 to ~=2.1

Updates the requirements on [pygithub](https://github.com/pygithub/pygithub) to permit the latest version.
- [Release notes](https://github.com/pygithub/pygithub/releases)
- [Changelog](https://github.com/PyGithub/PyGithub/blob/main/doc/changes.rst)
- [Commits](PyGithub/PyGithub@v1.57...v2.1.1)

---
updated-dependencies:
- dependency-name: pygithub
  dependency-type: direct:development
...

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

requirements-dev.txt

@@ -2,6 +2,6 @@
 black==23.9.1
 packaging==23.1
 pre-commit~=3.4
-PyGithub~=1.57
+PyGithub~=2.1
 pyupgrade~=3.13
 yamllint~=1.32