Avoid late require calls in potential hot spots

Ref: https://bugs.ruby-lang.org/issues/20641

Granted it's an upstream bug, but even without the bug `require`
isn't cheap. `ConfigurationFile` isn't that hot of a spot in
production, but in Active Record test suite it's called for
almost every test so with this Ruby 3.3 bug it account for significant
part of the test suite runtime.

Author: byroot

activesupport/lib/active_support/configuration_file.rb

@@ -33,8 +33,8 @@ def parse(context: nil, **options)
 
     private
       def read(content_path)
-        require "yaml"
-        require "erb"
+        require "yaml" unless defined?(YAML)
+        require "erb" unless defined?(ERB)
 
         File.read(content_path).tap do |content|
           if content.include?("\u00A0")