Update src/trio/_tests/test_exports.py

Co-authored-by: John Litborn <11260241+jakkdl@users.noreply.github.com>

Author: graingert

src/trio/_tests/test_exports.py

@@ -384,10 +384,7 @@ def lookup_symbol(symbol: str) -> dict[str, str]:
         elif tool == "mypy":
             # load the cached type information
             cached_type_info = cache_json["names"][class_name]
-            # previously this was an 'if' but it seems it's no longer possible
-            # for this cache to contain 'node', if this assert raises for you
-            # please let us know!
-            assert "node" not in cached_type_info
+            assert "node" not in cached_type_info, "previously this was an 'if' but it seems it's no longer possible for this cache to contain 'node', if this assert raises for you please let us know!"
             cached_type_info = lookup_symbol(cached_type_info["cross_ref"])
 
             assert "node" in cached_type_info