build: bump serde_json from 1.0.80 to 1.0.81 in /fuzz

Bumps [serde_json](https://github.com/serde-rs/json) from 1.0.80 to 1.0.81.
- [Release notes](https://github.com/serde-rs/json/releases)
- [Commits](https://github.com/serde-rs/json/compare/v1.0.80...v1.0.81)

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

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

fuzz/Cargo.lock

@@ -614,9 +614,9 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.80"
+version = "1.0.81"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f972498cf015f7c0746cac89ebe1d6ef10c293b94175a243a2d9442c163d9944"
+checksum = "9b7ce2b32a1aed03c558dc61a5cd328f15aff2dbc17daad8fb8af04d2100e15c"
 dependencies = [
  "itoa",
  "ryu",