Fix python shebang

The current shebang requires python 2 instead of python 3.

Trivial-Fix

Change-Id: I9172b43648c28e51edfd5d8695e750c18292ff90

Author: kajinamit

tools/run-tests.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (c) 2019 SUSE
 #