Fix the reading can write resolver test

This test wasn't correct. If we're calling `resolver.read` and want to
actually read from the replicas then the role would be reading not
writing. This was because the session store needed to be changed so that
we actually are "reading from the replicas" instead of reading from the
primary.

activerecord/test/cases/database_selector_test.rb

@@ -50,23 +50,21 @@ def test_read_from_replicas
     end
 
     def test_can_write_while_reading_from_replicas_if_explicit
-      @session_store[:last_write] = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session.convert_time_to_timestamp(Time.now)
+      @session_store[:last_write] = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session.convert_time_to_timestamp(Time.now - 5.seconds)
 
       resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver.new(@session)
 
       called = false
       resolver.read do
         called = true
-        assert ActiveRecord::Base.connected_to?(role: :writing)
-        assert_predicate ActiveRecord::Base.connection, :preventing_writes?
+        assert ActiveRecord::Base.connected_to?(role: :reading)
 
         ActiveRecord::Base.connected_to(role: :writing, prevent_writes: false) do
           assert ActiveRecord::Base.connected_to?(role: :writing)
           assert_not_predicate ActiveRecord::Base.connection, :preventing_writes?
         end
 
-        assert ActiveRecord::Base.connected_to?(role: :writing)
-        assert_predicate ActiveRecord::Base.connection, :preventing_writes?
+        assert ActiveRecord::Base.connected_to?(role: :reading)
       end
       assert called
     end