psbt: Use Amount::ZERO in unit test

We have a const for this, use it.

Internal change only.

bitcoin/src/psbt/mod.rs

@@ -2283,7 +2283,7 @@ mod tests {
             version: transaction::Version::TWO,
             lock_time: absolute::LockTime::ZERO,
             input: vec![TxIn::EMPTY_COINBASE, TxIn::EMPTY_COINBASE],
-            output: vec![TxOut { value: Amount::from_sat(0), script_pubkey: ScriptBuf::new() }],
+            output: vec![TxOut { value: Amount::ZERO, script_pubkey: ScriptBuf::new() }],
         };
         let mut psbt = Psbt::from_unsigned_tx(unsigned_tx).unwrap();