Fix build metadata rerun tracking

Author: sionsmith

build.rs

@@ -1,4 +1,13 @@
 fn main() {
+    println!("cargo:rerun-if-changed=.git/HEAD");
+    println!("cargo:rerun-if-changed=.git/packed-refs");
+
+    if let Ok(head) = std::fs::read_to_string(".git/HEAD") {
+        if let Some(ref_name) = head.strip_prefix("ref: ") {
+            println!("cargo:rerun-if-changed=.git/{}", ref_name.trim());
+        }
+    }
+
     let git_hash = std::process::Command::new("git")
         .args(["rev-parse", "--short", "HEAD"])
         .output()