Update pydantic requirement from ==2.8.* to ==2.9.* in /app (#1347)

Updates the requirements on [pydantic](https://github.com/pydantic/pydantic) to permit the latest version.
- [Release notes](https://github.com/pydantic/pydantic/releases)
- [Changelog](https://github.com/pydantic/pydantic/blob/main/HISTORY.md)
- [Commits](pydantic/pydantic@v2.8.0b1...v2.9.0)

---
updated-dependencies:
- dependency-name: pydantic
  dependency-type: direct:production
...

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

app/requirements.txt

@@ -1,7 +1,7 @@
 Flask==3.0.*
 Flask-HTTPAuth==4.8.*
 paho-mqtt== 2.1.*
-pydantic==2.8.*
+pydantic==2.9.*
 python-dotenv==1.0.*
 requests==2.32.*
 PyYAML==6.0.*