Add witness script for non-anchor static payment output psbt

[alecchendev]

Found some sort of regression I think (or maybe this was changed for a reason?), previously a static payment output would include the witness script like this, but doesn't anymore.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.60%. Comparing base (a952d2d) to head (6b738c6).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3352      +/-   ##
==========================================
- Coverage   89.61%   89.60%   -0.02%     
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  Files         127      127              
  Lines      103531   103534       +3     
  Branches   103531   103534       +3     
==========================================
- Hits        92782    92772      -10     
- Misses       8052     8059       +7     
- Partials     2697     2703       +6     

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[TheBlueMatt]

I don't think it ever changed. That code was added in https://github.com/lightningdevkit/rust-lightning/pull/2605/files#diff-da70679f6091fec0bb9157e1890b8bbe607fe9633d0e79a1f282c35ea8ad0fe2 and I vaguely recall discussion of not doing this but I don't see it on that PR now. Really the payment key isn't a "witness script" because a "witness script" is the script which gets run, not a public key. There's some discussion of it at https://github.com/murchandamus/bips/pull/1/files#r1571487623 but @murchandamus defines it as only for P2WSH so this doesn't make sense.

[alecchendev]

Oops yea realized this was actually just something in our fork that got changed when it was upstreamed in #2761. Never mind!