No longer use pathlib .suffix to check file extension

for client event schema files
.suffix is not included in importlib.resources APIs and so might not always work

Author: kiendang

jupyter_server/utils.py

@@ -268,7 +268,10 @@ def get_client_schema_files():
 
     files = chain.from_iterable(d.iterdir() for d in dirs if d is not None)
 
-    return (f for f in files if f.suffix in ('.json', '.yaml', '.yml'))
+    return (
+        f for f in files
+        if f.is_file() and os.path.splitext(f.name)[1] in ('.json', '.yaml', '.yml')
+    )
 
 
 def _is_iterable(x):