[WIP] Attempt to fix CI failure

Rails `main` is [currently][] set to `7.2.0.alpha`. However, `ci.yml`
uses `'main'` for the `RAILS_VERSION`.

[currently]: https://github.com/rails/rails/blob/5ab13c5a7798c2a9f96bebb1c68285dfb842d4f9/RAILS_VERSION

lib/rspec/rails/example/system_example_group.rb

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