adjusted python version number to updated python3 package

Signed-off-by: Joerg Seitter <adk@seitter.net>

mk/python3.mk

@@ -1,3 +1,3 @@
-PYTHON_VERSION=3.8
+PYTHON_VERSION=3.9
 PYTHON_LIBDIR:=$(STAGING_HOST_DIR)/usr/lib
 PYTHON:=${STAGING_HOST_DIR}/usr/bin/python3