95b7a95fc2 test: correct psbt used for regression test (Subhradeep Chakraborty)
Pull request description:
The `unknown` key used in the `Psbt` (in `serde_regression_psbt` test) is not really unknown. Also the `preimages` in the `Input` don't seem to be valid. Though they don't affect the tests because of the `serde::serialize`, the `Psbt` itself is invalid and hence this PR.
ACKs for top commit:
tcharding:
ACK 95b7a95fc2
apoelstra:
ACK 95b7a95fc2
Tree-SHA512: 275320bb273163364640351e55a3f16c34c1eef06e9dde79b72bf40187d313f037edb5e4544f4dce32fb8a7cc552504aa2e4d22a646c89a3dec022f917539219