gnutls: upgrade 3.7.7 -> 3.7.8

Changelog:
=========
** libgnutls: In FIPS140 mode, RSA signature verification is an approved
   operation if the key has modulus with known sizes (1024, 1280,
   1536, and 1792 bits), in addition to any modulus sizes larger than
   2048 bits, according to SP800-131A rev2.

** libgnutls: gnutls_session_channel_binding performs additional checks when
   GNUTLS_CB_TLS_EXPORTER is requested. According to RFC9622 4.2, the
   "tls-exporter" channel binding is only usable when the handshake is
   bound to a unique master secret (i.e., either TLS 1.3 or extended
   master secret extension is negotiated). Otherwise the function now
   returns error.

** libgnutls: usage of the following functions, which are designed to
   loosen restrictions imposed by allowlisting mode of configuration,
   has been additionally restricted. Invoking them is now only allowed
   if system-wide TLS priority string has not been initialized yet:
gnutls_digest_set_secure
gnutls_sign_set_secure
gnutls_sign_set_secure_for_certs
gnutls_protocol_set_enabled

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
(cherry picked from commit 858886aa)
Signed-off-by: Steve Sakoman <steve@sakoman.com>