requirements: update sphinxcontrib-htmlhelp requirement

Updates the requirements on [sphinxcontrib-htmlhelp](https://github.com/sphinx-doc/sphinxcontrib-htmlhelp) to permit the latest version.
- [Release notes](https://github.com/sphinx-doc/sphinxcontrib-htmlhelp/releases)
- [Changelog](https://github.com/sphinx-doc/sphinxcontrib-htmlhelp/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinxcontrib-htmlhelp@1.0.0...2.1.0)

---
updated-dependencies:
- dependency-name: sphinxcontrib-htmlhelp
  dependency-type: direct:production
...

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

broken_trans_deps.txt

@@ -42,6 +42,6 @@ beartype != 0.17.1; python_version == '3.9'
 # * sphinxcontrib-qthelp >=1.0.7
 sphinxcontrib-applehelp <1.0.8
 sphinxcontrib-devhelp <1.0.6
-sphinxcontrib-htmlhelp <2.0.5
+sphinxcontrib-htmlhelp <2.1.1
 sphinxcontrib-serializinghtml <1.1.10
 sphinxcontrib-qthelp <1.0.7