Fix type annotations examples (openai#496)

I fixed the type annotations errors for pydantic objects in some
examples as noted in openai#490 .

When running `make lint` the following error occurs "UP007 Use `X | Y`
for type annotations". If you know how to ignore it I will be happy to
edit the pull request, thanks.

Author: DanieleMorotti

pyproject.toml

@@ -15,6 +15,7 @@ dependencies = [
     "types-requests>=2.0, <3",
     "mcp>=1.6.0, <2; python_version >= '3.10'",
     "mkdocs-static-i18n>=1.3.0",
+    "eval-type-backport>=0.2.2",
 ]
 classifiers = [
     "Typing :: Typed",