Bump serde_json from 1.0.64 to 1.0.68 (#9783)

Bumps [serde_json](https://github.com/serde-rs/json) from 1.0.64 to 1.0.68.
- [Release notes](https://github.com/serde-rs/json/releases)
- [Commits](https://github.com/serde-rs/json/compare/v1.0.64...v1.0.68)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

substrate/Cargo.lock

@@ -8490,9 +8490,9 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.64"
+version = "1.0.68"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "799e97dc9fdae36a5c8b8f2cae9ce2ee9fdce2058c57a93e6099d919fd982f79"
+checksum = "0f690853975602e1bfe1ccbf50504d67174e3bcf340f23b5ea9992e0587a52d8"
 dependencies = [
  "itoa",
  "ryu",