build: bump once_cell from 1.12.0 to 1.12.1 in /fuzz

Bumps [once_cell](https://github.com/matklad/once_cell) from 1.12.0 to 1.12.1.
- [Release notes](https://github.com/matklad/once_cell/releases)
- [Changelog](https://github.com/matklad/once_cell/blob/master/CHANGELOG.md)
- [Commits](https://github.com/matklad/once_cell/compare/v1.12.0...v1.12.1)

---
updated-dependencies:
- dependency-name: once_cell
  dependency-type: indirect
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

fuzz/Cargo.lock

@@ -431,9 +431,9 @@ dependencies = [
 
 [[package]]
 name = "once_cell"
-version = "1.12.0"
+version = "1.12.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7709cef83f0c1f58f666e746a08b21e0085f7440fa6a29cc194d68aac97a4225"
+checksum = "ac8b1a9b2518dc799a2271eff1688707eb315f0d4697aa6b0871369ca4c4da55"
 
 [[package]]
 name = "option_parser"