Disambiguate some python shebang lines to be "python3"

Loonycyborg already uses these tools with Python 3.

The python launcher tool for Windows has magic handling for some shebang lines,
however `#!/bin/env python` isn't recognised without the `/usr`. Had the `/usr`
been included with the old code then these scripts would likely have been run
with Python 2.
https://docs.python.org/dev/using/windows.html#shebang-lines

utils/dockerbuilds/mingw/get_dlls.py

@@ -1,4 +1,4 @@
-#!/bin/env python
+#!/usr/bin/env python3
 
 import pefile, pathlib, shutil
 

utils/update_appdata

@@ -1,4 +1,4 @@
-#!/bin/env python
+#!/usr/bin/env python3
 
 import sys, requests, argparse
 from xml.dom import minidom