added back accidently removed code

lib/ansible/galaxy/collection/__init__.py

@@ -1306,6 +1306,7 @@ def _build_collection_tar(
 ):  # type: (...) -> str
     """Build a tar.gz collection artifact from the manifest data."""
     files_manifest_json = to_bytes(json.dumps(file_manifest, indent=True, sort_keys=True), errors='surrogate_or_strict')
+    collection_manifest['file_manifest_file']['chksum_sha256'] = secure_hash_s(files_manifest_json, hash_func=sha256)
     collection_manifest_json = to_bytes(json.dumps(collection_manifest, indent=True), errors='surrogate_or_strict')
 
     with _tempdir() as b_temp_path: