Change PKCS_RSA_PSS_SHA256 salt_len to 32

The default salt_len value for RSA PSS SHA256 is the current value,
20.
However, the only application that we currently know can use the
generated RSA PSS CSRs is Parsec https://github.com/parallaxsecond/parsec
which requires a salt length of 32 to work with OPENSSL.

 * Change this value to 32 to be compatible with Parsec.

On this topic, the spec states:
"When signing, it is RECOMMENDED that the parameters, except for
possibly saltLength, remain fixed for all usages of a given RSA key
pair"; and this is the value we are changing.

Signed-off-by: Tomás González <[email protected]>

rcgen/src/sign_algo.rs

@@ -160,7 +160,7 @@ pub(crate) mod algo {
 		params: SignatureAlgorithmParams::RsaPss {
 			// id-sha256 in https://datatracker.ietf.org/doc/html/rfc4055#section-2.1
 			hash_algorithm: &[2, 16, 840, 1, 101, 3, 4, 2, 1],
-			salt_length: 20,
+			salt_length: 32,
 		},
 	};