Bump marshmallow from 3.20.2 to 3.21.0

Bumps [marshmallow](https://github.com/marshmallow-code/marshmallow) from 3.20.2 to 3.21.0.
- [Changelog](https://github.com/marshmallow-code/marshmallow/blob/dev/CHANGELOG.rst)
- [Commits](marshmallow-code/marshmallow@3.20.2...3.21.0)

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

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

requirements.txt

@@ -7,7 +7,7 @@ feedgen==1.0.0
 gunicorn==21.2.0
 httpx==0.27.0
 jsonpatch==1.33
-marshmallow==3.20.2
+marshmallow==3.21.0
 pytest==8.0.2
 pytest-datadir==1.5.0
 rdflib==7.0.0