Bump babel from 2.14.0 to 2.15.0 in /docs

Bumps [babel](https://github.com/python-babel/babel) from 2.14.0 to 2.15.0.
- [Release notes](https://github.com/python-babel/babel/releases)
- [Changelog](https://github.com/python-babel/babel/blob/master/CHANGES.rst)
- [Commits](python-babel/babel@v2.14.0...v2.15.0)

---
updated-dependencies:
- dependency-name: babel
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

docs/requirements.txt

@@ -2,7 +2,7 @@ Jinja2==3.1.3
 MarkupSafe==2.1.5
 Pygments==2.17.2
 alabaster==0.7.16
-babel==2.14.0
+babel==2.15.0
 certifi==2024.2.2
 chardet==5.2.0
 commonmark==0.9.1