Make the output deterministic

Tests using randomized signatures were currently randomized. We need the
output of the script to be reproducible, so this won't do.

Force randomized signatures to use a specific RNG which is reset before
constructing each test case. This way, the script's output is reproducible.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

util/generate_mldsa_tests.py

@@ -45,6 +45,7 @@ class Key:
         self.public, self.secret = PURE[kl]._keygen_internal(seed)
 
     def sign_message(self, message: bytes, deterministic: bool) -> bytes:
+        PURE[self.kl].set_drbg_seed(bytes(48))
         return PURE[self.kl].sign(self.secret, message,
                                   deterministic=deterministic)