Fixed #20823 -- Typo in docs/ref/forms/validation.txt

docs/ref/forms/validation.txt

@@ -171,7 +171,7 @@ following guidelines:
 
 Putting it all together::
 
-    raise ValidationErrror(
+    raise ValidationError(
         _('Invalid value: %(value)s'),
         code='invalid',
         params={'value': '42'},