test: fix MiniWallet internal key derivation for tagged instances

Not every pseudorandom hash result is a valid x-only public key,
so the pubkey tweaking in the course of creating the output public
key would fail about every second time.

Fix this by treating the hash result as private key and calculate
the x-only public key out of that, to be used then as internal key.

Author: theStack

test/functional/test_framework/wallet.py

@@ -105,7 +105,7 @@ def __init__(self, test_node, *, mode=MiniWalletMode.ADDRESS_OP_TRUE, tag_name=N
             pub_key = self._priv_key.get_pubkey()
             self._scriptPubKey = key_to_p2pk_script(pub_key.get_bytes())
         elif mode == MiniWalletMode.ADDRESS_OP_TRUE:
-            internal_key = None if tag_name is None else hash256(tag_name.encode())
+            internal_key = None if tag_name is None else compute_xonly_pubkey(hash256(tag_name.encode()))[0]
             self._address, self._taproot_info = create_deterministic_address_bcrt1_p2tr_op_true(internal_key)
             self._scriptPubKey = address_to_scriptpubkey(self._address)