lddtree: raise min version to Python 3.8

We aren't using Python 3.6 anywhere anymore that I care about, so
raise the min version to 3.8.  Tools are dropping support for it
too which makes it difficult to reasonably support.

Signed-off-by: Mike Frysinger <[email protected]>

lddtree.py

@@ -51,7 +51,7 @@
 import sys
 from typing import Any, Dict, Iterable, List, Optional, Tuple, Union, cast
 
-assert sys.version_info >= (3, 6), f"Python 3.6+ required, but found {sys.version}"
+assert sys.version_info >= (3, 8), f"Python 3.8+ required, but found {sys.version}"
 
 # Disable import errors for all 3rd party modules.
 # pylint: disable=import-error