Bump babel from 2.3.4 to 2.9.1 in /openstack_requirements/tests/files

Bumps [babel](https://github.com/python-babel/babel) from 2.3.4 to 2.9.1.
- [Release notes](https://github.com/python-babel/babel/releases)
- [Changelog](https://github.com/python-babel/babel/blob/master/CHANGES)
- [Commits](python-babel/babel@2.3.4...v2.9.1)

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

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

openstack_requirements/tests/files/upper-constraints.txt

@@ -452,7 +452,7 @@ glance-store===0.20.0
 sphinx-testing===0.7.1
 dnspython===1.15.0
 oauthlib===2.0.1
-Babel===2.3.4
+Babel===2.9.1
 logutils===0.3.4.1
 scandir===1.5
 sphinxcontrib-fulltoc===1.1