notifications: Fix hash-named duplicate sound files in options.

Our hash-naming of production assets interacted badly with the "look
at files in a directory" algorithm used to determine what sound
options exist for the "notification sound" feature.  For lack of a
better solution, we fix this by excluding files with an extra `.` in
their name.

zerver/lib/actions.py

@@ -2853,6 +2853,10 @@ def get_available_notification_sounds() -> List[str]:
 
     for file_name in os.listdir(notification_sounds_path):
         root, ext = os.path.splitext(file_name)
+        if '.' in root:  # nocoverage
+            # Exclude e.g. zulip.abcd1234.ogg (generated by production hash-naming)
+            # to avoid spurious duplicates.
+            continue
         if ext == '.ogg':
             available_notification_sounds.append(root)