include both parsed values in the ProtocolError message

Author: Harshal96

src/h2/stream.py

@@ -1377,7 +1377,7 @@ def _initialize_content_length(self, headers: Iterable[Header]) -> None:
                 if content_length is None:
                     content_length = parsed_content_length
                 elif parsed_content_length != content_length:
-                    msg = "Conflicting content-length headers"
+                    msg = f"Conflicting content-length headers: {content_length} and {parsed_content_length}"
                     raise ProtocolError(msg)
 
         if content_length is None:

tests/test_invalid_content_lengths.py

@@ -105,7 +105,10 @@ def test_duplicate_conflicting_content_lengths(self, frame_factory, request_head
                 ("content-length", "16"),
             ],
         )
-        with pytest.raises(h2.exceptions.ProtocolError):
+        with pytest.raises(
+            h2.exceptions.ProtocolError,
+            match="Conflicting content-length headers: 15 and 16",
+        ):
             c.receive_data(headers.serialize())
 
         expected_frame = frame_factory.build_goaway_frame(