pep517 backend - Use correct import_module import (#80480)

changelogs/fragments/pep517-backend-import-fix.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - pep517 build backend - Use the documented ``import_module`` import from ``importlib``.

packaging/pep517_backend/_backend.py

@@ -9,7 +9,7 @@ import sys
 import typing as t
 from configparser import ConfigParser
 from contextlib import contextmanager, suppress
-from importlib.metadata import import_module
+from importlib import import_module
 from io import StringIO
 from pathlib import Path
 from shutil import copytree