build: bump bitflags from 1.2.1 to 1.3.1 in /fuzz

Bumps [bitflags](https://github.com/bitflags/bitflags) from 1.2.1 to 1.3.1.
- [Release notes](https://github.com/bitflags/bitflags/releases)
- [Changelog](https://github.com/bitflags/bitflags/blob/main/CHANGELOG.md)
- [Commits](https://github.com/bitflags/bitflags/compare/1.2.1...1.3.1)

---
updated-dependencies:
- dependency-name: bitflags
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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

fuzz/Cargo.lock

@@ -87,9 +87,9 @@ dependencies = [
 
 [[package]]
 name = "bitflags"
-version = "1.2.1"
+version = "1.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
+checksum = "2da1976d75adbe5fbc88130ecd119529cf1cc6a93ae1546d8696ee66f0d21af1"
 
 [[package]]
 name = "block_util"