Bump phonopy from 2.26.6 to 2.28.0

Bumps [phonopy](https://github.com/phonopy/phonopy) from 2.26.6 to 2.28.0.
- [Changelog](https://github.com/phonopy/phonopy/blob/develop/doc/changelog.md)
- [Commits](phonopy/phonopy@v2.26.6...v2.28.0)

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

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

pyproject.toml

@@ -38,7 +38,7 @@ Repository = "https://github.com/pyiron/atomistics"
 
 [project.optional-dependencies]
 phonopy = [
-    "phonopy==2.26.6",
+    "phonopy==2.28.0",
     "seekpath==2.1.0",
     "structuretoolkit==0.0.28",
 ]