pip: bump alabaster from 0.7.13 to 0.7.15 (#157)

Bumps [alabaster](https://github.com/sphinx-doc/alabaster) from 0.7.13 to 0.7.15.
- [Release notes](https://github.com/sphinx-doc/alabaster/releases)
- [Changelog](https://github.com/sphinx-doc/alabaster/blob/master/docs/changelog.rst)
- [Commits](sphinx-doc/alabaster@0.7.13...0.7.15)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -1,4 +1,4 @@
-alabaster==0.7.13
+alabaster==0.7.15
 Babel==2.14.0
 certifi==2023.11.17
 charset-normalizer==3.3.2