Suppress RuboCop offenses

This commit suppresses the following new RuboCop offenses:

```console
$ bundle exec rubocop
(snip)

rubocop-performance.gemspec:33:5: C: [Correctable] Gemspec/AddRuntimeDependency:
Use add_dependency instead of add_runtime_dependency.
  s.add_runtime_dependency('rubocop', '>= 1.48.1', '< 2.0')
    ^^^^^^^^^^^^^^^^^^^^^^
rubocop-performance.gemspec:34:5: C: [Correctable] Gemspec/AddRuntimeDependency:
Use add_dependency instead of add_runtime_dependency.
  s.add_runtime_dependency('rubocop-ast', '>= 1.31.1', '< 2.0')
    ^^^^^^^^^^^^^^^^^^^^^^

118 files inspected, 2 offenses detected, 2 offenses autocorrectable
```

rubocop-performance.gemspec

@@ -30,6 +30,6 @@ Gem::Specification.new do |s|
     'rubygems_mfa_required' => 'true'
   }
 
-  s.add_runtime_dependency('rubocop', '>= 1.48.1', '< 2.0')
-  s.add_runtime_dependency('rubocop-ast', '>= 1.31.1', '< 2.0')
+  s.add_dependency('rubocop', '>= 1.48.1', '< 2.0')
+  s.add_dependency('rubocop-ast', '>= 1.31.1', '< 2.0')
 end