Aurora Version Check called for non-aurora postgres databases

[deasthamgp]

https://github.com/DataDog/integrations-core/blob/2719f7dd6994f1e2c3c0be3cf69b11190dd2ea95/postgres/datadog_checks/postgres/postgres.py#L342

This line should be: if self._is_aurora: -> the function return from version_utils.py is a boolean value of FALSE (not aurora) or TRUE (is arurora) -> The current version of the line if self._is_aurora is NONE:-> causes the check to execute for every postgres database regardless of whether it's an Aurora Database or not.

Changing this to the suggested variation will execute the check when the value returned is TRUE and skip when FALSE.