lint: Fix code that evaded our lint checks for string % non-tuple.

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

zerver/lib/logging_util.py

@@ -23,7 +23,7 @@ class _RateLimitFilter:
 
         # Track duplicate errors
         duplicate = False
-        rate = getattr(settings, '%s_LIMIT' % self.__class__.__name__.upper(),
+        rate = getattr(settings, '%s_LIMIT' % (self.__class__.__name__.upper(),),
                        600)  # seconds
         if rate > 0:
             # Test if the cache works