Don't validate reserved words if the format doesn't match

Because it also won't match the sophisticated format we have for
detecting reserved names. We don't want to confuse the user with 2
error messages

app/validators/dynamic_path_validator.rb

@@ -198,6 +198,7 @@ class DynamicPathValidator < ActiveModel::EachValidator
   def validate_each(record, attribute, value)
     unless value =~ Gitlab::Regex.namespace_regex
       record.errors.add(attribute, Gitlab::Regex.namespace_regex_message)
+      return
     end
 
     if path_reserved_for_record?(record, value)