Correct 50-nonstop.conf to support QUIC tests under SPT threading models.

Correct 50-nonstop.conf to support QUIC tests under SPT threading models.

This fix also separates the FLOSS from SPT configurations which should not
have been conflated in the 3.0 series.

Related-to: #22588
Signed-off-by: Randall S. Becker <randall.becker@nexbridge.ca>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22697)