Kyber_py CCAPKE_Keygen function correction

to generate e, the correct is to use eta_2. Doesn't change much for advanced kyber types tho, but found it while studying.

Author: ncbor

src/kyber_py/kyber/kyber.py

@@ -168,7 +168,7 @@ def _cpapke_keygen(self):
         s_hat = s.to_ntt()
 
         # Generate the error vector e ∈ R^k
-        e, N = self._generate_error_vector(sigma, self.eta_1, N)
+        e, N = self._generate_error_vector(sigma, self.eta_2, N)
         e_hat = e.to_ntt()
 
         # Construct the public key