Pin Rust crate walkdir to =2.5.0 (rust-lang#1587)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

front_matter/Cargo.toml

@@ -9,4 +9,4 @@ serde = { version = "=1.0.219", features = ["derive"] }
 toml = "=0.8.20"
 
 [dev-dependencies]
-walkdir = "2.5.0"
+walkdir = "=2.5.0"