Restore ScriptBuf and Witness test imports

The v2 receive test module lost `ScriptBuf` and `Witness` from its
bitcoin import after two branches merged with a silent semantic
conflict. Commit 4548e25 shrank the import to `{Amount, FeeRate}`
because it deleted the code that used them, while PR #1718 (merged
against a stale base) added new test code that uses `ScriptBuf` and
`Witness`. The 3-way merge kept master's shrunken import alongside the
PR's new usages, breaking `cargo test` compilation on master.

Re-add both types to the import so the lib test build compiles.

Author: spacebear21

payjoin/src/core/receive/v2/mod.rs

@@ -1652,7 +1652,7 @@ pub(crate) fn pj_uri<'a>(
 pub mod test {
     use std::str::FromStr;
 
-    use bitcoin::{Amount, FeeRate};
+    use bitcoin::{Amount, FeeRate, ScriptBuf, Witness};
     use once_cell::sync::Lazy;
     use payjoin_test_utils::{
         BoxError, EXAMPLE_URL, ORIGINAL_PSBT, PARSED_ORIGINAL_PSBT, PARSED_PAYJOIN_PROPOSAL,