gh-85792: Update shebang to python3

Lib/encodings/rot_13.py

@@ -1,4 +1,3 @@
-#!/usr/bin/env python
 """ Python Character Mapping Codec for ROT13.
 
 This codec de/encodes from str to str.

Lib/idlelib/idle_test/example_noext

@@ -1,4 +1,2 @@
-#!usr/bin/env python
-
 def example_function(some_argument):
     pass

Parser/asdl_c.py

@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 """Generate C code from an ASDL description."""
 
 import sys

Tools/build/smelly.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Script checking that all symbols exported by libpython start with Py or _Py
 
 import os.path

Tools/wasm/emscripten/web_example/server.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 import argparse
 from http import server
 

Tools/wasm/emscripten/web_example/wasm_assets.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 """Create a WASM asset bundle directory structure.
 
 The WASM asset bundles are pre-loaded by the final WASM build. The bundle