File.exists? removed in Ruby 3.2

[SeanLF]

After upgrading to Ruby 3.2, we had the following error pop up in Sentry:

NoMethodError: undefined method `exists?' for File:Class (NoMethodError)

          File.delete(ssl_filename) if File.exists?(ssl_filename)
                                           ^^^^^^^^
Did you mean?  exist?
  from rubycas-client (2.3.9) lib/casclient/tickets/storage.rb:129:in `cleanup_service_session_lookup'

According to Ruby 3.2's changelogs, File.exists has been removed:

Removed methods
The following deprecated methods are removed.

[...]
File.exists? [Feature #17391]

---

There are two references to File.exists? in the codebase, which need to be updated to File.exist?

rubycas-client/lib/casclient/tickets/storage.rb

Lines 116 to 129 in 7b67c8f

	return IO.read(ssl_filename) if File.exists?(ssl_filename)
	end
	# Removes a stored relationship between a ServiceTicket and a local
	# Rails session id. This should be called when the session is being
	# closed.
	#
	# See #store_service_session_lookup.
	def cleanup_service_session_lookup(st)
	raise CASException, "No service_ticket specified." if st.nil?
	st = st.ticket if st.kind_of? ServiceTicket
	ssl_filename = filename_of_service_session_lookup(st)
	File.delete(ssl_filename) if File.exists?(ssl_filename)