TST: Investigate ResourceWarning unclosed file

[pllim]

Some tests complain about unclosed files. These are probably not worth fixing since those functions are not widely used anymore, if at all. But still, something to keep in mind.

lib/stsci/tools/tests/test_check_files.py::test_check_files
  .../tools/check_files.py:61: ResourceWarning: unclosed file <_io.FileIO name='.../tests/data/acs_test.fits' mode='rb' closefd=True>
    newfilelist = [hdul.filename() for hdul in newfilelist]

lib/stsci/tools/tests/test_check_files.py::test_check_files
  .../tools/check_files.py:39: ResourceWarning: unclosed file <_io.FileIO name='.../tools/tests/data/o4sp040b0_raw.fits' mode='rb' closefd=True>
    newfilelist, ivmlist = checkStisFiles(newfilelist, ivmlist)

lib/stsci/tools/tests/test_check_files.py::test_waivered_fits
  .../tools/convertwaiveredfits.py:563: ResourceWarning: unclosed file <_io.FileIO name='u40x010hm_c0f.fits' mode='rb' closefd=True>
    return func(*(waiveredObject,outputFileName,forceFileOutput,verbose))

lib/stsci/tools/tests/test_check_files.py::test_waivered_fits
  .../tools/check_files.py:61: ResourceWarning: unclosed file <_io.FileIO name='u40x010hm_c0h.fits' mode='rb+' closefd=True>
    newfilelist = [hdul.filename() for hdul in newfilelist]