When checking test vectors, handle RuntimeException in signing

This is better for playing around with the code. Now these
these exceptions can really be raised when the verification
during signing fails.

bip-0340/reference.py

@@ -122,7 +122,7 @@ def schnorr_sign(msg, seckey, aux_rand):
     sig = bytes_from_point(R) + bytes_from_int((k + e * d) % n)
     debug_print_vars()
     if not schnorr_verify(msg, bytes_from_point(P), sig):
-        raise RuntimeError('The signature does not pass verification.')
+        raise RuntimeError('The created signature does not pass verification.')
     return sig
 
 def schnorr_verify(msg, pubkey, sig):
@@ -173,13 +173,17 @@ def test_vectors():
                     print('   Expected key:', pubkey.hex().upper())
                     print('     Actual key:', pubkey_actual.hex().upper())
                 aux_rand = bytes.fromhex(aux_rand)
-                sig_actual = schnorr_sign(msg, seckey, aux_rand)
-                if sig == sig_actual:
-                    print(' * Passed signing test.')
-                else:
-                    print(' * Failed signing test.')
-                    print('   Expected signature:', sig.hex().upper())
-                    print('     Actual signature:', sig_actual.hex().upper())
+                try:
+                    sig_actual = schnorr_sign(msg, seckey, aux_rand)
+                    if sig == sig_actual:
+                        print(' * Passed signing test.')
+                    else:
+                        print(' * Failed signing test.')
+                        print('   Expected signature:', sig.hex().upper())
+                        print('     Actual signature:', sig_actual.hex().upper())
+                        all_passed = False
+                except RuntimeError as e:
+                    print(' * Signing test raised exception:', e)
                     all_passed = False
             result_actual = schnorr_verify(msg, pubkey, sig)
             if result == result_actual: