Merge #20292: test: Fix intermittent feature_taproot issue

fab900802d ci: Bump timeout factor (MarcoFalke)
50eb0c2512 Small improvements to the Taproot functional tests (Pieter Wuille)
fac865b72d test: Fix intermittent feature_taproot issue (MarcoFalke)
fa1dea19fc test: Fix deser issue in create_block (MarcoFalke)
fa762a3fd4 test: Remove unused unnamed parameter from block.serialize call (MarcoFalke)

Pull request description:

  This fixes three bugs. Also, fix some unrelated code style issues.

  Please refer to the commit messages for more information.

ACKs for top commit:
  laanwj:
    Code review ACK fab900802d

Tree-SHA512: 4e22c240cf345710f3b21fc63243126b90014b3656d0865ff87156e958dd1442e6572c6c0a5701dbbe503eee931a0ceb66eeeb3553137f3d1f5afd27a9f9cada

test/functional/test_framework/key.py

@@ -10,7 +10,6 @@ import csv
 import hashlib
 import os
 import random
-import sys
 import unittest
 
 from .util import modinv
@@ -22,6 +21,7 @@ def TaggedHash(tag, data):
     return hashlib.sha256(ss).digest()
 
 def xor_bytes(b0, b1):
+    assert len(b0) == len(b1)
     return bytes(x ^ y for (x, y) in zip(b0, b1))
 
 def jacobi_symbol(n, k):
@@ -523,7 +523,8 @@ class TestFrameworkKey(unittest.TestCase):
     def test_schnorr_testvectors(self):
         """Implement the BIP340 test vectors (read from bip340_test_vectors.csv)."""
         num_tests = 0
-        with open(os.path.join(sys.path[0], 'test_framework', 'bip340_test_vectors.csv'), newline='', encoding='utf8') as csvfile:
+        vectors_file = os.path.join(os.path.dirname(os.path.realpath(__file__)), 'bip340_test_vectors.csv')
+        with open(vectors_file, newline='', encoding='utf8') as csvfile:
             reader = csv.reader(csvfile)
             next(reader)
             for row in reader: