cleanup: address unnecessary_borrow lints reported by Clippy 1.66

Interestingly, the nightly release doesn't complain about this. One
instance in `test_working_copy.rs` is a bug in Clippy.

lib/src/simple_op_store.rs

@@ -60,7 +60,7 @@ fn upgrade_from_thrift(store_path: &Path) -> std::io::Result<()> {
     // Find the current operation head(s) of the operation log
     let op_heads_store_path = repo_path.join("op_heads");
     let mut old_op_heads = HashSet::new();
-    for entry in fs::read_dir(&op_heads_store_path)? {
+    for entry in fs::read_dir(op_heads_store_path)? {
         let basename = entry?.file_name();
         let op_id_str = basename.to_str().unwrap();
         if let Ok(op_id_bytes) = hex::decode(op_id_str) {

lib/tests/test_bad_locking.rs

@@ -45,7 +45,7 @@ fn merge_directories(left: &Path, base: &Path, right: &Path, output: &Path) {
         if child_left.is_dir() {
             sub_dirs.push(base_name.to_os_string());
         } else {
-            std::fs::copy(&child_left, &child_output).unwrap();
+            std::fs::copy(&child_left, child_output).unwrap();
         }
     }
     // Walk the base and find files removed in the right side, then remove them in
@@ -75,7 +75,7 @@ fn merge_directories(left: &Path, base: &Path, right: &Path, output: &Path) {
         } else if !child_base.exists() {
             // This overwrites the left side if that's been written. That's fine, since the
             // point of the test is that it should be okay for either side to win.
-            std::fs::copy(&child_right, &child_output).unwrap();
+            std::fs::copy(&child_right, child_output).unwrap();
         }
     }
     // Do the merge in subdirectories

lib/tests/test_working_copy.rs

@@ -401,6 +401,8 @@ fn test_snapshot_racy_timestamps(use_git: bool) {
     let wc = test_workspace.workspace.working_copy_mut();
     for i in 0..100 {
         {
+            // https://github.com/rust-lang/rust-clippy/issues/9778
+            #[allow(clippy::needless_borrow)]
             let mut file = OpenOptions::new()
                 .create(true)
                 .write(true)