Fix an error for Style/RedundantFormat

Follow-up to #13844 (comment).

This PR fixes an error for `Style/RedundantFormat`
when numeric placeholders is used in the template argument.

Author: koic

changelog/fix_an_error_for_style_redundant_format_cop.md

@@ -0,0 +1 @@
+* [#13857](https://github.com/rubocop/rubocop/pull/13857): Fix an error for `Style/RedundantFormat` when numeric placeholders is used in the template argument. ([@koic][])

lib/rubocop/cop/style/redundant_format.rb

@@ -160,7 +160,7 @@ def matching_argument?(sequence, argument)
         end
 
         def numeric?(argument)
-          argument.type?(:numeric, :str) ||
+          argument&.type?(:numeric, :str) ||
             rational_number?(argument) ||
             complex_number?(argument)
         end

spec/rubocop/cop/style/redundant_format_spec.rb

@@ -314,6 +314,12 @@
               #{method}('%{foo}', foo)
             RUBY
           end
+
+          it 'does not register an offense when given numeric placeholders in the template argument' do
+            expect_no_offenses(<<~RUBY)
+              #{method}('%<placeholder>d, %<placeholder>f', placeholder)
+            RUBY
+          end
         end
 
         context 'with an interpolated format string' do