schannel: enable ALPN support under WINE 6.0+

schannel: enable ALPN support under WINE 6.0+

ALPN support was announced in 5.6 (2020-04-10). It likely needs a WINE
built against GnuTLS 3.2.0 (2013-05-10) or upper (for macOS, GnuTLS was
made default in WINE 6.0.2). I could confirm ALPN working under 6.0.2
(2021-10-26).

https://www.winehq.org/announce/5.6
https://gitlab.winehq.org/wine/wine/-/commit/0527cf89fb907c330bc4fad3b135a1c85208fa9e
https://gitlab.winehq.org/wine/wine/-/blob/wine-5.6/dlls/secur32/schannel_gnutls.c
https://gitlab.winehq.org/wine/wine/-/blob/wine-5.6/dlls/secur32/tests/schannel.c

If you run into problems, open and Issue and disable ALPN manually with
`--no-alpn` or the equivalent for libcurl.

Ref: #983
Closes #16393