Bump sphinxcontrib-bibtex from 2.6.3 to 2.6.4 in the sphinx group

Bumps the sphinx group with 1 update: [sphinxcontrib-bibtex](https://github.com/mcmtroffaes/sphinxcontrib-bibtex).


Updates `sphinxcontrib-bibtex` from 2.6.3 to 2.6.4
- [Changelog](https://github.com/mcmtroffaes/sphinxcontrib-bibtex/blob/develop/CHANGELOG.rst)
- [Commits](mcmtroffaes/sphinxcontrib-bibtex@2.6.3...2.6.4)

---
updated-dependencies:
- dependency-name: sphinxcontrib-bibtex
  dependency-version: 2.6.4
  dependency-type: direct:development
  update-type: version-update:semver-patch
  dependency-group: sphinx
...

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

Author: dependabot[bot]