Consider selenium-webdriver version for Ruby 2.7

This commit addresses the Rails CI failure at 7-1-stable branch using Ruby 2.7
https://buildkite.com/rails/rails/builds/108575#019038c9-7c19-44e9-8c90-b257a3293450/1092-1106

Because selenium-webdriver >= 4.9.1 requires Ruby 3.0 then Gemfile of 7-1-stable branch
chooses the selenium-webdriver version based on the Ruby version.
rails#48847

Follow up rails@41844df

actionpack/test/dispatch/system_testing/driver_test.rb

@@ -113,13 +113,23 @@ class DriverTest < ActiveSupport::TestCase
     end
     driver.use
 
-    expected = {
-      "moz:firefoxOptions" => {
-        "args" => ["--host=127.0.0.1"],
-        "prefs" => { "remote.active-protocols" => 3, "browser.startup.homepage" => "http://www.seleniumhq.com/" }
-      },
-      "browserName" => "firefox"
-    }
+    if RUBY_VERSION < "3"
+      expected = {
+        "moz:firefoxOptions" => {
+          "args" => ["--host=127.0.0.1"],
+          "prefs" => { "browser.startup.homepage" => "http://www.seleniumhq.com/" }
+        },
+        "browserName" => "firefox"
+      }
+    else
+      expected = {
+        "moz:firefoxOptions" => {
+          "args" => ["--host=127.0.0.1"],
+          "prefs" => { "remote.active-protocols" => 3, "browser.startup.homepage" => "http://www.seleniumhq.com/" }
+        },
+        "browserName" => "firefox"
+      }
+    end
     assert_driver_capabilities driver, expected
   end
 
@@ -130,13 +140,23 @@ class DriverTest < ActiveSupport::TestCase
     end
     driver.use
 
-    expected = {
-      "moz:firefoxOptions" => {
-        "args" => ["-headless", "--host=127.0.0.1"],
-        "prefs" => { "remote.active-protocols" => 3, "browser.startup.homepage" => "http://www.seleniumhq.com/" }
-      },
-      "browserName" => "firefox"
-    }
+    if RUBY_VERSION < "3"
+      expected = {
+        "moz:firefoxOptions" => {
+          "args" => ["-headless", "--host=127.0.0.1"],
+          "prefs" => {  "browser.startup.homepage" => "http://www.seleniumhq.com/" }
+        },
+        "browserName" => "firefox"
+      }
+    else
+      expected = {
+        "moz:firefoxOptions" => {
+          "args" => ["-headless", "--host=127.0.0.1"],
+          "prefs" => { "remote.active-protocols" => 3, "browser.startup.homepage" => "http://www.seleniumhq.com/" }
+        },
+        "browserName" => "firefox"
+      }
+    end
     assert_driver_capabilities driver, expected
   end