Fix parsing list of extra non-body parameters

fastapi/dependencies/utils.py

@@ -790,9 +790,16 @@ def request_params_to_args(
         processed_keys.add(alias or field.alias)
         processed_keys.add(field.name)
 
-    for key, value in received_params.items():
+    for key in received_params.keys():
         if key not in processed_keys:
-            params_to_process[key] = value
+            if hasattr(received_params, "getlist"):
+                value = received_params.getlist(key)
+                if isinstance(value, list) and (len(value) == 1):
+                    params_to_process[key] = value[0]
+                else:
+                    params_to_process[key] = value
+            else:
+                params_to_process[key] = received_params.get(key)
 
     if single_not_embedded_field:
         field_info = first_field.field_info

tests/test_tutorial/test_header_param_models/test_tutorial003.py

@@ -77,7 +77,7 @@ def test_header_param_model_no_underscore(client: TestClient):
                             "user-agent": "testclient",
                             "save-data": "true",
                             "if-modified-since": "yesterday",
-                            "x-tag": "two",
+                            "x-tag": ["one", "two"],
                         },
                     }
                 )