fix(ci): repoint codeql-action at a SHA that exists (#46)

`github/codeql-action@29b1f65c1f735799893313399435a59f54045865` is
pinned here but **exists in no repository** — the GitHub API returns 422
for it.

CodeQL therefore could not start: the run graph fails to build and the
job reports `startup_failure`, so this repository has had **no CodeQL
scanning at all**.

Repointed at `4187e74d05793876e9989daffde9c3e66b4acd07`, which is what
the `v3` tag currently resolves to (v3.37.3), verified against the API.

Found while auditing the estate: the same non-existent SHA was pinned in
**104 repositories**, so CodeQL was dead across nearly all of them.

----
## Summary by Gitar

- **CI updates:**
- Updated `guix.scm` package definition for `squisher-corpus` and
license
- Added `actions: read` permission across multiple GitHub workflow files

<sub>This will update automatically on new commits.</sub>

---------

Signed-off-by: Jonathan D.A. Jewell <6759885+hyperpolymath@users.noreply.github.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: hyperpolymath