Fix python shebang

Signed-off-by: Cristian Le <cristian.le@mpsd.mpg.de>

Author: LecrisUT

test-suite/clean_tests

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 """
 This script runs the tests either asking interactively if you want to run 
 only one, or runs them all with the proper command-line options.

test-suite/run_tests

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 """
 This script runs the tests either asking interactively if you want to run 
 only one, or runs them all with the proper command-line options.