docs: fix fastapi ext demo (#776)

Signed-off-by: Joël Séguillon <joel.seguillon@gmail.com>
Co-authored-by: Elena Kolevska <elena-kolevska@users.noreply.github.com>

Author: jseguillon

daprdocs/content/en/python-sdk-docs/python-sdk-extensions/python-fastapi.md

@@ -47,7 +47,7 @@ class RawEventModel(BaseModel):
 
 class User(BaseModel):
     id: int
-    name = 'Jane Doe'
+    name: str
 
 class CloudEventModel(BaseModel):
     data: User