Don't write bytecode on MacOS

MacOS packages are signed and checked on each run.  Since Python lives
inside the package, adding byte code will break the package signature

(cherry picked from commit 5881471a52)

scripting/python_scripting.cpp

@@ -156,6 +156,10 @@ bool SCRIPTING::scriptingSetup()
   #endif
 #elif defined( __WXMAC__ )
 
+    // Prevent Mac builds from generating JIT versions as this will break
+    // the package signing
+    wxSetEnv( "PYTHONDONTWRITEBYTECODE", "1" );
+
     // Add default paths to PYTHONPATH
     wxString pypath;