meson: Fix permissions of installed scripts

configure_file preserves the attributes, so the templates need to be
executable for the (installed) outputs to be executable.

https://bugzilla.gnome.org/show_bug.cgi?id=787671

gobject/meson.build

@@ -76,7 +76,6 @@ python_tools_conf.set('VERSION', glib_version)
 python_tools_conf.set('PYTHON', python.path())
 
 foreach tool: python_tools
-  # FIXME: Ensure we set the appropriate permissions
   tool_bin = configure_file(
     input : tool + '.in',
     output : tool,