Bump deps/coqutil from f12ff02 to 126561c

Bumps [deps/coqutil](https://github.com/mit-plv/coqutil) from `f12ff02` to `126561c`.
- [Release notes](https://github.com/mit-plv/coqutil/releases)
- [Commits](mit-plv/coqutil@f12ff02...126561c)

---
updated-dependencies:
- dependency-name: deps/coqutil
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>