Bump django-stubs-ext from 5.2.8 to 5.2.9 in /backend (baserow#4638)

Bumps [django-stubs-ext](https://github.com/sponsors/typeddjango) from 5.2.8 to 5.2.9.
- [Commits](https://github.com/sponsors/typeddjango/commits)

---
updated-dependencies:
- dependency-name: django-stubs-ext
  dependency-version: 5.2.9
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

backend/pyproject.toml

@@ -146,7 +146,7 @@ dev = [
     "graphviz==0.21",
     "pytest-cov==7.0.0",
     "django-stubs==5.2.8",
-    "django-stubs-ext==5.2.8",
+    "django-stubs-ext==5.2.9",
     "mypy==1.19.1",
     "mypy-extensions==1.1.0",
     "ipython",