Threading bug

[baentsch]

Describe the bug
A seriously multicore machine crashes liboqs with the exit message "5: double free or corruption (!prev)"

To Reproduce
Steps to reproduce the behavior:

1. Build liboqs main on a fast, multicore machine
2. Execute oqs-provider ctest

Expected behavior
All tests pass.

Actual behaviour
Error message "5: double free or corruption (!prev)" appears after all tests completed

Environment (please complete the following information):

• OS: Ubuntu 22
• OpenSSL version: 3.2.0-dev
• Compiler version used: gcc-11.3.
• Build variables used: none
• liboqs version: main

Additional context
Initial gdb trace seems to indicate error occurring in oqs_free_ossl_objects. Looks like the static pointers need to be NULLed......