signet: miner skips PSBT step for OP_TRUE

test/functional/test_framework/blocktools.py

@@ -80,6 +80,9 @@ DIFF_4_N_BITS = 0x1c3fffc0
 DIFF_4_TARGET = int(DIFF_1_TARGET / 4)
 assert_equal(uint256_from_compact(DIFF_4_N_BITS), DIFF_4_TARGET)
 
+# From BIP325
+SIGNET_HEADER = b"\xec\xc7\xda\xa2"
+
 def nbits_str(nbits):
     return f"{nbits:08x}"