Fix the intermittent lhash_test failure on Windows

Fix the intermittent lhash_test failure on Windows

We must set pending_delete before the actual deletion as another inserting
or deleting thread can pick up the delete callback before the
ossl_ht_write_unlock() call.

This can happen only if no read locks are pending and only on Windows where
we do not use the write mutex to get the callback list.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/26152)