cache-tree: use index state repository in trace2 calls

trace2 calls in cache-tree.c use the global 'the_repository',
even though cache_tree_update() has access to an explicit
repository pointer via 'istate->repo'.

Using the global repository can result in incorrect trace2
output when multiple repository instances are in use, as
events may be attributed to the wrong repository.

Use 'istate->repo' in cache_tree_update() to ensure correct
repository attribution.

Other call sites are left unchanged as they do not have
access to a repository instance.

Signed-off-by: Jayesh Daga <jayeshdaga99@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: jayesh0104

cache-tree.c

@@ -488,12 +488,12 @@ int cache_tree_update(struct index_state *istate, int flags)
 		prefetch_cache_entries(istate, must_check_existence);
 
 	trace_performance_enter();
-	trace2_region_enter("cache_tree", "update", the_repository);
+	trace2_region_enter("cache_tree", "update", istate->repo);
 	transaction = odb_transaction_begin(the_repository->objects);
 	i = update_one(istate->cache_tree, istate->cache, istate->cache_nr,
 		       "", 0, &skip, flags);
 	odb_transaction_commit(transaction);
-	trace2_region_leave("cache_tree", "update", the_repository);
+	trace2_region_leave("cache_tree", "update", istate->repo);
 	trace_performance_leave("cache_tree_update");
 	if (i < 0)
 		return i;