refactor(store/fs): address clippy

Change-Id: I28d60263ef672942940656caa8e0f9d20cc6b7d7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10231
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/store/src/fs/tests.rs

@@ -871,7 +871,7 @@ async fn check_attributes() {
     assert_eq!(fixtures::BLOB_A.len() as u64, metadata_file.len());
     // directories should have their "size" as filesize
     assert_eq!(
-        fixtures::DIRECTORY_WITH_KEEP.size() as u64,
+        { fixtures::DIRECTORY_WITH_KEEP.size() },
         metadata_directory.size()
     );