build: bump serde from 1.0.138 to 1.0.139

Bumps [serde](https://github.com/serde-rs/serde) from 1.0.138 to 1.0.139.
- [Release notes](https://github.com/serde-rs/serde/releases)
- [Commits](https://github.com/serde-rs/serde/compare/v1.0.138...v1.0.139)

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

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

net_util/Cargo.toml

@@ -11,7 +11,7 @@ libc = "0.2.126"
 log = "0.4.17"
 net_gen = { path = "../net_gen" }
 rate_limiter = { path = "../rate_limiter" }
-serde = "1.0.138"
+serde = "1.0.139"
 versionize = "0.1.6"
 versionize_derive = "0.1.4"
 virtio-bindings = "0.1.0"