Fix failing fixture support test on Rails main

This test is failing since setup_fixtures was made private in
rails/rails@29fe344.

It was added in 82241e9 to exercise the
call to `name` in Rails' `run_in_transaction?` method:
https://github.com/rails/rails/blob/b4ab1f19d8bcc4639c7379b560f000f01753b5b0/activerecord/lib/active_record/test_fixtures.rb#L101

However since 9272757, RSpec Rails
overrides `run_in_transaction?`, so `name` is no longer called. We can
get even better integration coverage of an example group with
use_transactional_tests set to false by actually running an example.

Author: eugeneius

spec/rspec/rails/fixture_support_spec.rb

@@ -39,14 +39,21 @@ module RSpec::Rails
       end
     end
 
-    it "will allow #setup_fixture to run successfully" do
-      group = RSpec::Core::ExampleGroup.describe do
-        include FixtureSupport
+    context "with use_transactional_tests set to false" do
+      it "does not wrap the test in a transaction" do
+        allow(RSpec.configuration).to receive(:use_transactional_fixtures) { true }
+        group = RSpec::Core::ExampleGroup.describe do
+          include FixtureSupport
 
-        self.use_transactional_tests = false
-      end
+          self.use_transactional_tests = false
+
+          it "doesn't run in transaction" do
+            expect(ActiveRecord::Base.connection.transaction_open?).to eq(false)
+          end
+        end
 
-      expect { group.new.setup_fixtures }.to_not raise_error
+        expect_to_pass(group)
+      end
     end
 
     it "handles namespaced fixtures" do