Use headless driver for next Rails release

In the next release of Rails, the default driver was switched from
`:chrome` to `:headless_chrome` as see in: rails/rails#50512
This is to ensure the new [ci template][] will "work out of the box".

However, this will not work with applications using `rspec-rails`, since
it still defaults to `:selenium`. Instead, GitHub actions will fail with
the following error:

```
Selenium::WebDriver::Error::SessionNotCreatedError:
            session not created: Chrome failed to start: exited normally.
              (session not created: DevToolsActivePort file doesn't exist)
              (The process started from chrome location /usr/bin/google-chrome is no longer running, so ChromeDriver is assuming that Chrome has crashed.)
```

[ci template]: https://github.com/rails/rails/blob/main/railties/lib/rails/generators/rails/app/templates/github/ci.yml.tt

lib/rspec/rails/example/system_example_group.rb

@@ -137,7 +137,11 @@ def initialize(*args, &blk)
           self.class.before do
             # A user may have already set the driver, so only default if driver
             # is not set
-            driven_by(:selenium) unless @driver
+            if ::Rails::VERSION::STRING.to_f >= 7.2
+              driven_by(:selenium_chrome_headless) unless @driver
+            else
+              driven_by(:selenium) unless @driver
+            end
           end
         end
 

spec/rspec/rails/example/system_example_group_spec.rb

@@ -70,6 +70,18 @@ module RSpec::Rails
       end
     end
 
+    describe '#driver', if: ::Rails::VERSION::STRING.to_f >= 7.2 do
+      it 'uses :selenium_chrome_headless driver by default' do
+        group = RSpec::Core::ExampleGroup.describe do
+          include SystemExampleGroup
+        end
+        example = group.new
+        group.hooks.run(:before, :example, example)
+
+        expect(Capybara.current_driver).to eq :selenium_chrome_headless
+      end
+    end
+
     describe '#after' do
       it 'sets the :extra_failure_lines metadata to an array of STDOUT lines' do
         allow(Capybara::Session).to receive(:instance_created?).and_return(true)