Add comment and simplify hiberfil_sys test

Author: ChrisDenton

library/std/src/fs/tests.rs

@@ -1535,13 +1535,14 @@ fn read_large_dir() {
     }
 }
 
+/// Test the fallback for getting the metadata of files like hiberfil.sys that
+/// Windows holds a special lock on, preventing normal means of querying
+/// metadata. See #96980.
 #[test]
 #[cfg(windows)]
 fn hiberfil_sys() {
-    // Get the system drive, which is usually `C:`.
-    let mut hiberfil = crate::env::var("SystemDrive").unwrap();
-    hiberfil.push_str(r"\hiberfil.sys");
+    let hiberfil = r"C:\hiberfil.sys";
 
-    fs::metadata(&hiberfil).unwrap();
-    fs::symlink_metadata(&hiberfil).unwrap();
+    fs::metadata(hiberfil).unwrap();
+    fs::symlink_metadata(hiberfil).unwrap();
 }