CentOS 9: Disable unit tests dependent on puppet-postgresql

The puppt-postgresql module does not support CentOS 9 yet and requires
some version parameters to be run on CentOS 9. This change disables
unit tests requiring that module, until the module supports CentOS 9.

Change-Id: I58f9719cfcd2b823c66de70b2109e0481baf767c

spec/classes/mistral_db_postgresql_spec.rb

@@ -40,7 +40,10 @@ describe 'mistral::db::postgresql' do
         }))
       end
 
-      it_configures 'mistral::db::postgresql'
+      # TODO(tkajinam): Remove this once puppet-postgresql supports CentOS 9
+      unless facts[:osfamily] == 'RedHat' and facts[:operatingsystemmajrelease].to_i >= 9
+        it_configures 'mistral::db::postgresql'
+      end
     end
   end