Upgrade phf to v0.12 (#448)

Author: paolobarbolini

strum/Cargo.toml

@@ -17,7 +17,7 @@ rust-version = "1.66.1"
 
 [dependencies]
 strum_macros = { path = "../strum_macros", optional = true, version = "0.27.1" }
-phf = { version = "0.11", features = ["macros"], optional = true }
+phf = { version = "0.12", features = ["macros"], optional = true }
 
 [dev-dependencies]
 strum_macros = { path = "../strum_macros" }