[nrf fromtree] twister: Fix TypeError at get_installed_packages

Fix confusing `TypeError: 'type' object is not subscriptable`
at _get_installed_packages() if twister runs on python version < 3.9

Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>
(cherry picked from commit b8bed5b)

scripts/pylib/twister/twisterlib/environment.py

@@ -16,7 +16,7 @@
 from datetime import datetime, timezone
 from importlib import metadata
 from pathlib import Path
-from typing import Generator
+from typing import Generator, List
 
 from twisterlib.coverage import supported_coverage_formats
 
@@ -49,7 +49,7 @@ def _get_installed_packages() -> Generator[str, None, None]:
         yield dist.metadata['Name']
 
 
-installed_packages: list[str] = list(_get_installed_packages())
+installed_packages: List[str] = list(_get_installed_packages())
 PYTEST_PLUGIN_INSTALLED = 'pytest-twister-harness' in installed_packages