Stop using an obsolete method of Net::HTTP (#8408)

https://docs.ruby-lang.org/en/2.7.0/Net/HTTP.html#method-c-Proxy

Net::HTTP::Proxy is an obsolete method, so replaced it with
Net::HTTP.new as the doc above says

rb/lib/selenium/server.rb

@@ -74,7 +74,7 @@ def download(required_version)
 
         begin
           File.open(download_file_name, 'wb') do |destination|
-            net_http.start('selenium-release.storage.googleapis.com') do |http|
+            net_http_start('selenium-release.storage.googleapis.com') do |http|
               resp = http.request_get("/#{required_version[/(\d+\.\d+)\./, 1]}/#{download_file_name}") do |response|
                 total = response.content_length
                 progress = 0
@@ -111,7 +111,7 @@ def download(required_version)
 
       def latest
         require 'rexml/document'
-        net_http.start('selenium-release.storage.googleapis.com') do |http|
+        net_http_start('selenium-release.storage.googleapis.com') do |http|
           versions = REXML::Document.new(http.get('/').body).root.get_elements('//Contents/Key').map do |e|
             e.text[/selenium-server-standalone-(\d+\.\d+\.\d+)\.jar/, 1]
           end
@@ -120,16 +120,16 @@ def latest
         end
       end
 
-      def net_http
+      def net_http_start(address, &block)
         http_proxy = ENV['http_proxy'] || ENV['HTTP_PROXY']
 
         if http_proxy
           http_proxy = "http://#{http_proxy}" unless http_proxy.start_with?('http://')
           uri = URI.parse(http_proxy)
 
-          Net::HTTP::Proxy(uri.host, uri.port)
+          Net::HTTP.start(address, nil, uri.host, uri.port, &block)
         else
-          Net::HTTP
+          Net::HTTP.start(address, &block)
         end
       end
     end

rb/lib/selenium/webdriver/remote/http/default.rb

@@ -132,8 +132,7 @@ def new_http_client
 
               proxy = URI.parse(url)
 
-              clazz = Net::HTTP::Proxy(proxy.host, proxy.port, proxy.user, proxy.password)
-              clazz.new(server_url.host, server_url.port)
+              Net::HTTP.new(server_url.host, server_url.port, proxy.host, proxy.port, proxy.user, proxy.password)
             else
               Net::HTTP.new server_url.host, server_url.port
             end

rb/spec/unit/selenium/server_spec.rb

@@ -124,11 +124,11 @@ module Selenium
 
     it 'automatically repairs http_proxy settings that do not start with http://' do
       with_env('http_proxy' => 'proxy.com') do
-        expect(Selenium::Server.net_http.proxy_address).to eq('proxy.com')
+        expect(Selenium::Server.net_http_start('example.com', &:proxy_address)).to eq('proxy.com')
       end
 
       with_env('HTTP_PROXY' => 'proxy.com') do
-        expect(Selenium::Server.net_http.proxy_address).to eq('proxy.com')
+        expect(Selenium::Server.net_http_start('example.com', &:proxy_address)).to eq('proxy.com')
       end
     end