Add release note for listunspent P2WSH change

doc/release-notes-14481.md

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+Low-level RPC changes
+----------------------
+
+The `listunspent` RPC has been modified so that it also returns `witnessScript`,
+the witness script in the case of a P2WSH or P2SH-P2WSH output.
+
+The `signrawtransactionwithkey` and `signrawtransactionwithwallet` RPCs have been
+modified so that they also optionally accept a `witnessScript`, the witness script in the
+case of a P2WSH or P2SH-P2WSH output. This is compatible with the change to `listunspent`.