When using `CURLOPT_PINNEDPUBLICKEY` option with libcurl or `--pinnedpubkey`
with the curl tool,curl should check the public key of the server certificate
to verify the peer.

This check was skipped in a certain condition that would then make curl allow
the connection without performing the proper check, thus not noticing a
possible impostor. To skip this check, the connection had to be done with QUIC
with ngtcp2 built to use GnuTLS and the user had to explicitly disable the
standard certificate verification.

When doing multi-threaded LDAPS transfers (LDAP over TLS) with libcurl,
changing TLS options in one thread would inadvertently change them globally
and therefore possibly also affect other concurrently setup transfers.

Disabling certificate verification for a specific transfer could
unintentionally disable the feature for other threads as well.

When an OAuth2 bearer token is used for an HTTP(S) transfer, and that transfer
performs a cross-protocol redirect to a second URL that uses an IMAP, LDAP,
POP3 or SMTP scheme, curl might wrongly pass on the bearer token to the new
target host.

When doing TLS related transfers with reused easy or multi handles and
altering the  `CURLSSLOPT_NO_PARTIALCHAIN` option, libcurl could accidentally
reuse a CA store cached in memory for which the partial chain option was
reversed. Contrary to the user's wishes and expectations. This could make
libcurl find and accept a trust chain that it otherwise would not.

When doing SSH-based transfers using either SCP or SFTP, and setting the
known_hosts file, libcurl could still mistakenly accept connecting to hosts
*not present* in the specified file if they were added as recognized in the
libssh *global* known_hosts file.

When doing SSH-based transfers using either SCP or SFTP, and asked to do
public key authentication, curl would wrongly still ask and authenticate using
a locally running SSH agent.