s4:scripting: Ensure generated error definition files are closed after use

s4:scripting: Ensure generated error definition files are closed after use

This helps to avoid warnings like this one:

/data/samba/source4/scripting/bin/gen_hresult.py:178: ResourceWarning: unclosed file <_io.TextIOWrapper name='/data/samba/bin/default/libcli/util/hresult.c' mode='w' encoding='UTF-8'>
  main()
ResourceWarning: Enable tracemalloc to get the object allocation traceback

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>