Adapt gix-config/gix-object benches to changes in criterion

`criterion` 0.6.0 deprecates `criterion::black_box()`, preferring
`std::hint::black_box()` (which `criterion::black_box()` now
consists of a call to).

This commit makes the recommended switch, in benches for
`gix-config` and `gix-object` where `criterion::black_box()` was
used, to `std::hint::black_box()`, fixing new clippy errors.

Fuzz tests have also been using `black_box()`, but they already
imported it from `std::hint`, and thus need no corresponding fix.

Author: EliahKagan

gix-config/benches/large_config_file.rs

@@ -1,5 +1,6 @@
-use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use criterion::{criterion_group, criterion_main, Criterion};
 use gix_config::{parse::Events, File};
+use std::hint::black_box;
 
 fn gix_config(c: &mut Criterion) {
     c.bench_function("GitConfig large config file", |b| {

gix-object/benches/decode_objects.rs

@@ -1,4 +1,5 @@
-use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use criterion::{criterion_group, criterion_main, Criterion};
+use std::hint::black_box;
 
 fn parse_commit(c: &mut Criterion) {
     c.bench_function("CommitRef(sig)", |b| {

gix-object/benches/edit_tree.rs

@@ -1,6 +1,6 @@
-use std::{cell::RefCell, rc::Rc};
+use std::{cell::RefCell, hint::black_box, rc::Rc};
 
-use criterion::{black_box, criterion_group, criterion_main, Criterion, Throughput};
+use criterion::{criterion_group, criterion_main, Criterion, Throughput};
 use gix_hash::ObjectId;
 use gix_hashtable::hash_map::Entry;
 use gix_object::{tree, tree::EntryKind, Tree, WriteTo};