Use python3 as the interpreter instead of python (ie v2)

This fixes lintian warning "unusual-interpreter".

Part of the Debian edition of FreeCAD since 2023.

src/Mod/TechDraw/TDTest/DLeaderRText.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 # test script for TechDraw module

src/Mod/TechDraw/TDTest/DrawHatchTest.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 

src/Mod/TechDraw/TDTest/DrawViewDetailTest.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 # test script for DrawViewDetail

src/Mod/TechDraw/TDTest/DrawViewPartTest.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 # basic test script for TechDraw module

src/Mod/TechDraw/TDTest/TDPyTest.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 # basic test script for TechDraw Py functions migrated from Drawing