gh-158313: Clear the OpenSSL error queue when ssl raises OSError

[lazerg]

The two ERR_LIB_SYS branches in PySSL_SetError return early and skip the ERR_clear_error() call that every other path makes. The entry then stays on the thread's error queue, and SSL_get_error() picks it up on the next I/O call on any socket in that thread, so the same OSError is raised again and again. This clears the queue in both branches, like the e == 0 branch already does.

The test fails on main with BrokenPipeError from the second connection.

Fixes #158313

• Issue: ssl: PySSL_SetError leaves the ERR_LIB_SYS entry on the OpenSSL error queue, so every later SSL I/O on that thread fails with the same OSError #158313