Fix occasional assertion failure when storing properties

Fix occasional assertion failure when storing properties

Fixes #18631

The store lock does not prevent concurrent access to the
property cache, because there are multiple stores.

We drop the newly created entry and use the exisiting one
if there is one already.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19762)

(cherry picked from commit 92a25e24e6ec9735dea9ec645502cb075a5f8d24)