Hide default gems warnings for Ruby 3.4.

These omit warnings with Ruby 3.3 and are required for Ruby 3.4. We'll
fix them when we're upgrading to 3.4 instead.

Library/Homebrew/warnings.rb

@@ -13,6 +13,7 @@ module Warnings
       # <!-- vale off -->
       %r{warning: please see https://github\.com/whitequark/parser#compatibility-with-ruby-mri\.},
       # <!-- vale on -->
+      %{warning: .+\.rb was loaded from the standard library, but will no longer be part of the default gems since Ruby \d+\.\d+\.\d+\.},
     ],
   }.freeze