Only load from cgi what is required for Ruby 3.5

In Ruby 3.5 most of the `cgi` gem will be removed. Only the various escape/unescape methods will be retained by default.

https://bugs.ruby-lang.org/issues/21258

Author: Earlopain

google-cloud-storage/lib/google/cloud/storage/file/signer_v2.rb

@@ -15,7 +15,7 @@
 
 require "addressable/uri"
 require "base64"
-require "cgi"
+require "cgi/escape"
 require "openssl"
 require "google/cloud/storage/errors"
 

google-cloud-storage/lib/google/cloud/storage/file/signer_v4.rb

@@ -14,7 +14,7 @@
 
 
 require "addressable/uri"
-require "cgi"
+require "cgi/escape"
 require "openssl"
 require "google/cloud/storage/errors"