[rubygems/rubygems] Fix test warnings introduced by recent CGI changes

They read like this:

```
/home/runner/work/rubygems/rubygems/bundler/tmp/gems/base/ruby/3.4.0/gems/cgi-0.5.0.beta2/lib/cgi/util.rb:13: warning: method redefined; discarding old rfc1123_date
/opt/hostedtoolcache/Ruby/3.4.3/x64/lib/ruby/3.4.0/cgi/util.rb:225: warning: previous definition of rfc1123_date was here
/home/runner/work/rubygems/rubygems/bundler/tmp/gems/base/ruby/3.4.0/gems/cgi-0.5.0.beta2/lib/cgi/util.rb:34: warning: method redefined; discarding old pretty
/opt/hostedtoolcache/Ruby/3.4.3/x64/lib/ruby/3.4.0/cgi/util.rb:246: warning: previous definition of pretty was here
/home/runner/work/rubygems/rubygems/bundler/tmp/gems/base/ruby/3.4.0/gems/cgi-0.5.0.beta2/lib/cgi/escape.rb:16: warning: method redefined; discarding old escape
/home/runner/work/rubygems/rubygems/bundler/tmp/gems/base/ruby/3.4.0/gems/cgi-0.5.0.beta2/lib/cgi/escape.rb:29: warning: method redefined; discarding old unescape
/home/runner/work/rubygems/rubygems/bundler/tmp/gems/base/ruby/3.4.0/gems/cgi-0.5.0.beta2/lib/cgi/util.rb:13: warning: method redefined; discarding old rfc1123_date
/opt/hostedtoolcache/Ruby/3.4.3/x64/lib/ruby/3.4.0/cgi/util.rb:225: warning: previous definition of rfc1123_date was here
/home/runner/work/rubygems/rubygems/bundler/tmp/gems/base/ruby/3.4.0/gems/cgi-0.5.0.beta2/lib/cgi/util.rb:34: warning: method redefined; discarding old pretty
/opt/hostedtoolcache/Ruby/3.4.3/x64/lib/ruby/3.4.0/cgi/util.rb:246: warning: previous definition of pretty was here
/home/runner/work/rubygems/rubygems/bundler/tmp/gems/base/ruby/3.4.0/gems/cgi-0.5.0.beta2/lib/cgi/escape.rb:16: warning: method redefined; discarding old escape
/home/runner/work/rubygems/rubygems/bundler/tmp/gems/base/ruby/3.4.0/gems/cgi-0.5.0.beta2/lib/cgi/escape.rb:29: warning: method redefined; discarding old unescape
```

The problem is that `rspec` loads `erb` for its configuration, which
loads `cgi/util` from system gems.

Then our tests change the `$LOAD_PATH` to make test gems installed in
tmp visible to `require`, and then they all require `cgi` as a
transitive dependency of `rack-test`, this time from `tmp` gems. This
causes system and test specific copies to be mixed together and these
warnings to be printed, but we have also observed failures in some tests
with errors like

> class variable @@accept_charset of CGI::Util is overtaken by CGI::Escape

This changes should also fix those failures.

The fix is to require all of `rack-test` (including `cgi`) before we
have changed the `$LOAD_PATH`. Because the `$LOAD_PATH` is unchanged,
RubyGems respects the version of `cgi` activated by RSpec, avoiding the
double loads.

ruby/rubygems@34e75465c6

Author: deivid-rodriguez

spec/bundler/commands/ssl_spec.rb

@@ -8,7 +8,7 @@
 
 RSpec.describe "bundle doctor ssl" do
   before(:each) do
-    require_rack
+    require_rack_test
     require_relative "../support/artifice/helpers/endpoint"
 
     @dummy_endpoint = Class.new(Endpoint) do

spec/bundler/install/gems/dependency_api_fallback_spec.rb

@@ -3,7 +3,7 @@
 RSpec.describe "gemcutter's dependency API" do
   context "when Gemcutter API takes too long to respond" do
     before do
-      require_rack
+      require_rack_test
 
       port = find_unused_port
       @server_uri = "http://127.0.0.1:#{port}"

spec/bundler/install/gems/gemfile_source_header_spec.rb

@@ -31,7 +31,7 @@
   private
 
   def setup_server
-    require_rack
+    require_rack_test
     @port = find_unused_port
     @server_uri = "http://127.0.0.1:#{@port}"
 

spec/bundler/install/gems/mirror_probe_spec.rb

@@ -7,7 +7,7 @@
   let(:host) { "127.0.0.1" }
 
   before do
-    require_rack
+    require_rack_test
     setup_server
     setup_mirror
   end

spec/bundler/support/helpers.rb

@@ -515,11 +515,11 @@ def with_env_vars(env_hash, &block)
       end
     end
 
-    def require_rack
-      # need to hack, so we can require rack
+    def require_rack_test
+      # need to hack, so we can require rack for testing
       old_gem_home = ENV["GEM_HOME"]
       ENV["GEM_HOME"] = Spec::Path.base_system_gem_path.to_s
-      require "rack"
+      require "rack/test"
       ENV["GEM_HOME"] = old_gem_home
     end