utils/diffconfig: use python3 explicitly

Python 2 is EOL sice 2020 [1], it's still available on distros, but may
not be installed by default (as being replaced by python3). A
compatibility symlink python -> python3 may not be installed either.

Convert the shebang line to the usual /usr/bin/env based line.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

utils/diffconfig

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 #
 # diffconfig - a tool to compare .config files.
 #