SSL Endpoint has been shutdown by Heroku

[mars]

Changelog entry: https://devcenter.heroku.com/changelog-items/2280

The Heroku SSL Endpoints add-on is deprecated and will be retired as of today: October 18, 2021. As part of the End of Life process, there will be service degradations beginning next week as the add-on is removed from the Heroku Ecosystem.

Our acceptance tests can no longer pass, because of test failures with heroku_cert, based on SSL Endpoint.

This provider already supports the newer SNI-based heroku_ssl resource, which has been the preferred mechanism since its implementation.

This issue is notice that we will be removing this end-of-life functionality from this provider.