test: fix keys_to_multisig_script (P2MS) helper for n/k > 16

The helper assumes that the n and k values have to be provided as a
single byte push operation, which is only possible for values up to 16.
Fix that by passing the numbers directly to the CScript list, where it's
automatically converted to minimally-encoded pushes (see class
method `CScript.__coerce_instance`, branch `isinstance(other, int)`).

In case of 17..20, this means that the data-pushes are done with two
bytes using OP_PUSH1 (0x01), e.g. for n=20: 0x01,0x14

test/functional/test_framework/script_util.py

@@ -5,7 +5,6 @@
 """Useful Script constants and utils."""
 from test_framework.script import (
     CScript,
-    CScriptOp,
     OP_0,
     OP_CHECKMULTISIG,
     OP_CHECKSIG,
@@ -49,10 +48,8 @@ def keys_to_multisig_script(keys, *, k=None):
     if k is None:  # n-of-n multisig by default
         k = n
     assert k <= n
-    op_k = CScriptOp.encode_op_n(k)
-    op_n = CScriptOp.encode_op_n(n)
     checked_keys = [check_key(key) for key in keys]
-    return CScript([op_k] + checked_keys + [op_n, OP_CHECKMULTISIG])
+    return CScript([k] + checked_keys + [n, OP_CHECKMULTISIG])
 
 
 def keyhash_to_p2pkh_script(hash):