As of mbedTLS 3.6.0 TLSv1.3 is enabled by default and certificate verification
is now mandatory. Our default configuration does not do verification, so
downgrade to 1.2 in these situations to avoid breaking it.

ref: https://github.com/Mbed-TLS/mbedtls/issues/7075Signed-off-by: Anton Khirnov <anton@khirnov.net>