Bump cython from 0.29.27 to 0.29.28 (#685)

Bumps [cython](https://github.com/cython/cython) from 0.29.27 to 0.29.28.
- [Release notes](https://github.com/cython/cython/releases)
- [Changelog](https://github.com/cython/cython/blob/master/CHANGES.rst)
- [Commits](cython/cython@0.29.27...0.29.28)

---
updated-dependencies:
- dependency-name: cython
  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/cython.txt

@@ -1 +1 @@
-cython==0.29.27
+cython==0.29.28