dist/tools: Use /usr/bin/env to lookup Python.

Fixes some Python scripts which didn't use `/usr/bin/env`.

dist/tools/bmp/bmp.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 # Copyright (C) 2019 Otto-von-Guericke-Universität Magdeburg
 #

dist/tools/ci/can_fast_ci_run.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 """
 Command line utility to check if only a subset of board / application combinations
 need to be build in the CI

dist/tools/compile_commands/compile_commands.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 """
 Command line utility to generate compile_commands.json for RIOT applications
 """

dist/tools/pyterm/testbeds/testbeds.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python2
+#!/usr/bin/env python2
 # -*- coding: utf-8 -*-
 
 # Copyright (C) 2014  Philipp Rosenkranz <philipp.rosenkranz@fu-berlin.de>

dist/tools/suit/suit-manifest-generator/setup.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 # ----------------------------------------------------------------------------
 # Copyright 2020 ARM Limited or its affiliates

dist/tools/suit/suit-manifest-generator/suit_tool/parse.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 # ----------------------------------------------------------------------------
 # Copyright 2019 ARM Limited or its affiliates

dist/tools/suit/suit-manifest-generator/suit_tool/sign.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 # ----------------------------------------------------------------------------
 # Copyright 2019 ARM Limited or its affiliates

dist/tools/usb-serial/ttys.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 """
 Command line utility to list and filter TTYs
 """