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/api.rb

@@ -4,7 +4,10 @@
 require "api/analytics"
 require "api/cask"
 require "api/formula"
+require "warnings"
+Warnings.ignore :default_gems do
   require "base64" # TODO: Add this to the Gemfile or remove it before moving to Ruby 3.4.
+end
 require "extend/cachable"
 
 module Homebrew

Library/Homebrew/dev-cmd/contributions.rb

@@ -2,7 +2,10 @@
 # frozen_string_literal: true
 
 require "abstract_command"
+require "warnings"
+Warnings.ignore :default_gems do
   require "csv"
+end
 
 module Homebrew
   module DevCmd

Library/Homebrew/warnings.rb

@@ -14,6 +14,9 @@ module Warnings
       %r{warning: please see https://github\.com/whitequark/parser#compatibility-with-ruby-mri\.},
       # <!-- vale on -->
     ],
+    default_gems:  [
+      /warning: .+\.rb was loaded from the standard library, .+ default gems since Ruby \d+\.\d+\.\d+\./,
+    ],
   }.freeze
 
   def self.ignore(*warnings)