✨ Add support for forbidding extra form fields with Pydantic models (#12134)

Co-authored-by: Sofie Van Landeghem <svlandeg@users.noreply.github.com>

fastapi/dependencies/utils.py

@@ -789,6 +789,9 @@ async def _extract_form_body(
             value = serialize_sequence_value(field=field, value=results)
         if value is not None:
             values[field.name] = value
+    for key, value in received_body.items():
+        if key not in values:
+            values[key] = value
     return values