remove forgotten exclamation point

Author: h-vetinari

pandas/core/strings.py

@@ -2289,7 +2289,7 @@ def cat(self, others=None, sep=None, na_rep=None, join=None):
                     or (x.dtype == 'float' and x.isna().all()))
                for x in others):
             raise TypeError('Can only concatenate list-likes containing only '
-                            'strings (or missing values)!')
+                            'strings (or missing values)')
 
         if join is None and warn:
             warnings.warn("A future version of pandas will perform index "