Don't run PostgreSQL integration tests on Ruby 3.2 in CI

They are occasionally resulting in a segfault when trying to
create an OpenSSL cipher when testing the column_encryption
plugin.

Rakefile

@@ -158,11 +158,8 @@ task :spec_ci=>[:spec_core, :spec_model, :spec_plugin, :spec_core_ext] do
     ENV['SEQUEL_MYSQL_URL'] = "mysql2://#{mysql_host}/sequel_test?user=root#{mysql_password}&useSSL=false"
   end
 
-  if RUBY_VERSION >= '2.3'
-    Rake::Task['spec_postgres'].invoke
-  end
-
   if RUBY_VERSION >= '2.4'
+    Rake::Task['spec_postgres'].invoke
     Rake::Task['spec_sqlite'].invoke
     Rake::Task['spec_mysql'].invoke
   end