Bump pydata-sphinx-theme from 0.14.4 to 0.15.4

Bumps [pydata-sphinx-theme](https://github.com/pydata/pydata-sphinx-theme) from 0.14.4 to 0.15.4.
- [Release notes](https://github.com/pydata/pydata-sphinx-theme/releases)
- [Changelog](https://github.com/pydata/pydata-sphinx-theme/blob/main/RELEASE.md)
- [Commits](pydata/pydata-sphinx-theme@v0.14.4...v0.15.4)

---
updated-dependencies:
- dependency-name: pydata-sphinx-theme
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

docs/requirements.txt

@@ -3,4 +3,4 @@ Sphinx>=4.5
 sphinx-book-theme
 myst-parser
 breathe>=4.34
-pydata-sphinx-theme==0.14.4
+pydata-sphinx-theme==0.15.4