Bump deps/coqutil from e395373 to 421da12

Bumps [deps/coqutil](https://github.com/mit-plv/coqutil) from `e395373` to `421da12`.
- [Release notes](https://github.com/mit-plv/coqutil/releases)
- [Commits](mit-plv/coqutil@e395373...421da12)

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

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