pip: bump sphinxcontrib-serializinghtml from 1.1.7 to 1.1.9

Bumps [sphinxcontrib-serializinghtml](https://github.com/sphinx-doc/sphinxcontrib-serializinghtml) from 1.1.7 to 1.1.9.
- [Release notes](https://github.com/sphinx-doc/sphinxcontrib-serializinghtml/releases)
- [Changelog](https://github.com/sphinx-doc/sphinxcontrib-serializinghtml/blob/master/CHANGES)
- [Commits](sphinx-doc/sphinxcontrib-serializinghtml@1.1.7...1.1.9)

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

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

requirements.txt

@@ -25,7 +25,7 @@ sphinxcontrib-devhelp==1.0.4
 sphinxcontrib-htmlhelp==2.0.3
 sphinxcontrib-jsmath==1.0.1
 sphinxcontrib-qthelp==1.0.3
-sphinxcontrib-serializinghtml==1.1.7
+sphinxcontrib-serializinghtml==1.1.9
 tqdm==4.66.1
 translate-toolkit==3.10.0
 urllib3==1.26.16