packager: use id instead of hex attrib since hex is removed in pygit 1.16

Author: m4rc1e

Lib/gftools/packager/__init__.py

@@ -423,7 +423,7 @@ def traverse(
         tree = repo.get(tree_oid)
         try:
             entry = tree[subtree_name]
-            existing_subtree = repo.get(entry.hex)
+            existing_subtree = repo.get(entry.id)
             sub_treebuilder = repo.TreeBuilder(existing_subtree)
         except KeyError:
             sub_treebuilder = repo.TreeBuilder()