Reverted String Class .to_a monkey patch

[haadfida]

.to_a method has been removed from the String class since Ruby 1.9 reference: https://stackoverflow.com/a/4465629/12131035
Rails caching code works with the assumption that .to_a can not be called on strings.

The following snippet below in the file Activesupport-6.0.3.2/lib/active_support/cache.rb, ends up in infinite recursion is .to_a method is called on Strings.

def expanded_version(key)
case
when key.respond_to?(:cache_version) then key.cache_version.to_param
when key.is_a?(Array) then key.map { |element| expanded_version(element) }.compact.to_param
when key.respond_to?(:to_a) then expanded_version(key.to_a)
end
end

This change is needed to ensure that rails and ruby code works as intended.