tls: fix legacy SecurePair session resumption

This seems to have been broken ever since its introduction 5 years ago
in commit 75ea11fc ("tls: introduce asynchronous `newSession`") and
no one complained but that's not going to stop me from fixing it anyway
because otherwise I can't write a regression test for issue #26428.

Refs: https://github.com/nodejs/node/issues/26428

PR-URL: https://github.com/nodejs/node/pull/26452
Fixes: https://github.com/nodejs/node/issues/26428


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>