Signed key type fix
Use the correct SIGNED_KEY_TYPE value for signing->link certs
Our code was using [01] as for the key type of signed->link certs,
which was incorrect. The value should be [03], to indicate that the
value as the SHA256 of an x.509 cert.
Fortunately, nothing cares about this value, so there shouldn't be
compatibility issues.
This fixes part of #40124 (closed) ; there is also a torspec fix.