[Bugfix] Resolve PSBT parsing error when signing Nested Segwit p2sh-p2wpkh

[newtonick]

Description

only treat p2sh as multisig and don't include p2sh-p2wpkh

This pull request is categorized as a:

• [ ] New feature
• [x] Bug fix
• [ ] Code refactor
• [ ] Documentation
• [ ] Other

Checklist

• [x] I’ve run pytest and made sure all unit tests pass before sumbitting the PR

If you modified or added functionality/workflow, did you add new unit tests?

• [ ] No, I’m a fool
• [x] Yes
• [ ] N/A

I have tested this PR on the following platforms/os:

• [x] Raspberry Pi OS Manual Build
• [ ] SeedSigner OS on a Pi0/Pi0W board
• [ ] Other

Note: Keep your changes limited in scope; if you uncover other issues or improvements along the way, ideally submit those as a separate PR. The more complicated the PR the harder to review, test, and merge.

[jdlcdl]

Confirming:

On current dev at 0f329f6f w/o this pr: after scanning a single-sig nested-segwit PSBT and selecting its seed:

• System Error, psbt_parser.py 293, in _parse_multisig, Not a multisig script

With this pr, scanning, review and signing work for me.