build: bump autogen-agentchat in /src/backend in the python-deps group

Bumps the python-deps group in /src/backend with 1 update: autogen-agentchat.


Updates `autogen-agentchat` from 0.4.0.dev12 to 0.7.5

---
updated-dependencies:
- dependency-name: autogen-agentchat
  dependency-version: 0.7.5
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: python-deps
...

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

Author: dependabot[bot]

src/backend/requirements.txt

@@ -1,6 +1,6 @@
 fastapi
 uvicorn
-autogen-agentchat==0.4.0.dev12
+autogen-agentchat==0.7.5
 azure-cosmos
 azure-identity
 python-dotenv