Suppress a new RuboCop offense

Follow up rubocop/rubocop#12383

This commit suppresses the following new RuboCop offense:

```console
$ bundle exec rubocop
(snip)

lib/rubocop/cop/rails/validation.rb:54:44: W: [Correctable] Lint/SymbolConversion: Unnecessary symbol conversion; use :"validates_#{p}_of" instead.
        RESTRICT_ON_SEND = TYPES.map { |p| "validates_#{p}_of".to_sym }.freeze
                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^

292 files inspected, 1 offense detected, 1 offense autocorrectable
```

lib/rubocop/cop/rails/validation.rb

@@ -51,7 +51,7 @@ class Validation < Base
           uniqueness
         ].freeze
 
-        RESTRICT_ON_SEND = TYPES.map { |p| "validates_#{p}_of".to_sym }.freeze
+        RESTRICT_ON_SEND = TYPES.map { |p| :"validates_#{p}_of" }.freeze
         ALLOWLIST = TYPES.map { |p| "validates :column, #{p}: value" }.freeze
 
         def on_send(node)