Improve tests (and maybe more) to assure parallel worktree tests are deterministic

At least so that tests deal with hardly avoidable non-determinism and there
are no spurious failures.

Author: Byron

gix-worktree/tests/worktree/checkout.rs

@@ -256,7 +256,6 @@ fn keep_going_collects_results() {
         opts,
         "make_mixed_without_submodules",
         |_id| {
-            dbg!(_id);
             !matches!(
                 count.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |current| {
                     (current < 2).then_some(current + 1)
@@ -292,10 +291,11 @@ fn keep_going_collects_results() {
 
     if multi_threaded() {
         let actual = dir_structure(&destination);
-        if actual.len() != 3 {
-            dbg!(destination.into_path());
-        }
-        assert_eq!(actual.len(), 3);
+        assert!(
+            (2..=3).contains(&actual.len()),
+            "it's 3 most of the time, but can be 2 of the 'empty' file is missing as the object couldn't be accessed.\
+             It's unclear why there isn't more, as it would keep going"
+        );
     } else {
         assert_eq!(
             stripped_prefix(&destination, &dir_structure(&destination)),
@@ -481,7 +481,6 @@ fn checkout_index_in_tmp_dir_opts(
             if allow_return_object(oid) {
                 odb.find_blob(oid, buf)
             } else {
-                dbg!(oid);
                 Err(gix_odb::find::existing_object::Error::NotFound { oid: oid.to_owned() })
             }
         },