bip-0374: fix challenge generation, use correct G

Both generating and verifying a proof allows for specifying a custom
generator point G. But that custom generator point was not passed into
the dleq_challenge function, resulting in the default (secp256k1)
generator point to be used. This lead to the test vectors being
incorrect.

bip-0374/reference.py

@@ -64,7 +64,7 @@ def dleq_generate_proof(
         return None
     R1 = k * G
     R2 = k * B
-    e = dleq_challenge(A, B, C, R1, R2, m)
+    e = dleq_challenge(A, B, C, R1, R2, m, G=G)
     s = (k + e * a) % GE.ORDER
     proof = e.to_bytes(32, "big") + s.to_bytes(32, "big")
     if not dleq_verify_proof(A, B, C, proof, G=G, m=m):
@@ -89,7 +89,7 @@ def dleq_verify_proof(
     R2 = s * B + (-e * C)
     if R2.infinity:
         return False
-    if e != dleq_challenge(A, B, C, R1, R2, m):
+    if e != dleq_challenge(A, B, C, R1, R2, m, G=G):
         return False
     return True