Unexisting function `_ssl__SSLContext_security_level_set` is referenced in source code

# Bug report

### Bug description:

https://github.com/python/cpython/blob/v3.15.0a1/Modules/clinic/_ssl.c.h#L1571

Introduced in #124993

This is documented as read-only attribute

https://docs.python.org/3/library/ssl.html#ssl.SSLContext.security_level

### CPython versions tested on:

3.15

### Operating systems tested on:

_No response_