BIP-340: fix `lift_x` calls in test vector generation script #1729

The lift_x function in the BIP and the reference implementation expect an integer to be passed rather than a byte array.

Can be tested with:

$ python3 test-vectors.py > expected.csv
$ diff test-vectors.csv expected.csv

On master, the first call fails with

Traceback (most recent call last):
  File "/home/thestack/bips/bip-0340/test-vectors.py", line 267, in <module>
    vector0(),
    ^^^^^^^^^
  File "/home/thestack/bips/bip-0340/test-vectors.py", line 30, in vector0
    pubkey_point = lift_x(pubkey)
                   ^^^^^^^^^^^^^^
  File "/home/thestack/bips/bip-0340/reference.py", line 72, in lift_x
    if x >= p:
       ^^^^^^
TypeError: '>=' not supported between instances of 'bytes' and 'int'

cc: @real-or-random, @jonasnick, @sipa

utACK 7d921e33148bac865ef84860f61a3a2eba233c7d This was apparently overlooked in 3998dbbc8a3ab3bfabb1b2e90a4840ad93a84adb

Thanks!

ACK 7d921e33148bac865ef84860f61a3a2eba233c7d

Thanks @theStack