cd712e8 ci: attest results of guix builds (pasta)

Pull request description:

  ## Issue being fixed or feature implemented
  This simply adds attestations to guix results by GitHub. This way, not only can someone verify that all us developers agree, but also that GitHub hosted runners agree :)

  ## What was done?
  Add actions/attest-build-provenance to guix-build CI

  ## How Has This Been Tested?
  see: https://github.com/PastaPastaPasta/dash/actions/runs/11239755631

  ## Breaking Changes
  None

  ## Checklist:
    _Go over all the following points, and put an `x` in all the boxes that apply._
  - [x] I have performed a self-review of my own code
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have added or updated relevant unit/integration/functional/e2e tests
  - [ ] I have made corresponding changes to the documentation
  - [x] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  UdjinM6:
    utACK cd712e8

Tree-SHA512: b590ee2cf29aa57f78cb68c22d5327e8c9272d63d523c3b64fbbdffabb90981a6b6505c5f511bde19310ea1d8c96fc6d181359a7d7a0672612473110cbe079ef

d627a6e chore: bump version to 21.1.1 (pasta)
5f9700c docs: release notes for v21.1.1 (pasta)
1c00726 Merge #6277: chore: add builder key for kittywhiskers (pasta)
a2bc0f1 Merge #6290: chore: update pasta gpg key to reflect new subkeys (pasta)
167608c Merge #6338: ci: attest results of guix builds (pasta)
6fb4e49 Merge #6197: ci: always build guix, save artifacts (pasta)
c0ca93c Merge #6340: fix: make 6336 compile in v21.1.x branch, using older CHECK_NONFATAL functionality (pasta)
bb96df4 Merge #6336: fix: rpc getblock and getblockstats for blocks with withdrawal transactions (asset unlock) (pasta)
8e70262 Merge #6131: feat: make a support of Qt app to show Platform transfer Tx (pasta)
80ed279 Merge #6328: backport: bitcoin#30131, bitcoin#23258, bitcoin#30504 - fix bild for Ubuntu 24.10 + clang (pasta)
bd772fb Merge #6229: fix: `creditOutputs` in AssetLock tx json output should be an array of objects, not debug strings (pasta)
9bf39a9 Merge #6222: fix: adjust payee predictions after mn_rr activation, add tests (pasta)
87bebfc Merge #6219: fix: correct is_snapshot_cs in VerifyDB (pasta)
a4e6b8a Merge #6208: fix: persist coinjoin denoms options from gui over restarts (pasta)

Pull request description:

  ## Issue being fixed or feature implemented
  See commits, backports, release notes, version bump

  ## What was done?

  ## How Has This Been Tested?

  ## Breaking Changes

  ## Checklist:
    _Go over all the following points, and put an `x` in all the boxes that apply._
  - [ ] I have performed a self-review of my own code
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have added or updated relevant unit/integration/functional/e2e tests
  - [ ] I have made corresponding changes to the documentation
  - [ ] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  knst:
    utACK d627a6e
  kwvg:
    ACK d627a6e
  UdjinM6:
    utACK d627a6e
  ogabrielides:
    utACK d627a6e

Tree-SHA512: cde7e40760e16e9f48da8149c3742d18a34029b057405e4d55b87110da96acbcd19b47280451dd7b5ad1ccfc91fde655452cf5f0f0d1e01a41b4c685337c64b8