Update phf_codegen requirement from 0.11 to 0.12

Updates the requirements on [phf_codegen](https://github.com/rust-phf/rust-phf) to permit the latest version.
- [Release notes](https://github.com/rust-phf/rust-phf/releases)
- [Changelog](https://github.com/rust-phf/rust-phf/blob/master/RELEASE_PROCESS.md)
- [Commits](rust-phf/rust-phf@phf_codegen-v0.11.1...v0.12.1)

---
updated-dependencies:
- dependency-name: phf_codegen
  dependency-version: 0.12.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

codegen/Cargo.toml

@@ -4,7 +4,7 @@ version = "0.1.0"
 authors = ["Steven Fackler <sfackler@gmail.com>"]
 
 [dependencies]
-phf_codegen = "0.11"
+phf_codegen = "0.12"
 regex = "1.0"
 marksman_escape = "0.1"
 linked-hash-map = "0.5"