get-bz-attachments: switch to python3

Nothing left to do, just switch the interpreter.

Change-Id: I6a0ff0a019a66f6baf39794c853655f273676ea2
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/161261
Tested-by: Thorsten Behrens <thorsten.behrens@allotropia.de>
Reviewed-by: Thorsten Behrens <thorsten.behrens@allotropia.de>

bin/get-bugzilla-attachments-by-mimetype

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 #
 # This file is part of the LibreOffice project.