DOC: Fix spaces and brackets in ValueError message for option_context. (#22121)

Author: pvanmulbregt

pandas/core/config.py

@@ -391,7 +391,7 @@ class option_context(object):
     def __init__(self, *args):
         if not (len(args) % 2 == 0 and len(args) >= 2):
             raise ValueError('Need to invoke as'
-                             'option_context(pat, val, [(pat, val), ...)).')
+                             ' option_context(pat, val, [(pat, val), ...]).')
 
         self.ops = list(zip(args[::2], args[1::2]))