Fix ShellBang Python Analysis

Do not assume a location of the python interpreter.

Author: ax3l

Examples/Modules/laser_injection_from_file/analysis.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python
 
 # This file is part of the WarpX automated test suite. It is used to test the
 # injection of a laser pulse from an external binary file.

Examples/Modules/relativistic_space_charge_initialization/analysis.py

@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#!/usr/bin/env python
 """
 This script checks the space-charge initialization routine, by
 verifying that the space-charge field of a Gaussian beam corresponds to

Examples/Modules/space_charge_initialization/analysis.py

@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#!/usr/bin/env python
 """
 This script checks the space-charge initialization routine, by
 verifying that the space-charge field of a Gaussian beam corresponds to