Failed to load Vega spectrum when running stsynphot unit tests

[zacharyburnett]

Steps that can reproduce the error:

1. run stsynphot tests in the Build and test environments workflow

2. the following error happens:

   https://github.com/spacetelescope/stenv/actions/runs/4621154067/jobs/8172491792#step:11:22

   E   astropy.utils.exceptions.AstropyUserWarning: Failed to load Vega spectrum from /tmp/trds/calspec/alpha_lyr_stis_010.fits; Functionality involving Vega will be cripped: FileNotFoundError(2, 'No such file or directory')
   

Previously, it looks like this error was a warning:
https://github.com/spacetelescope/stenv/actions/runs/4324015155/jobs/7551034165#step:11:54

/home/runner/work/stenv/stenv/stsynphot/stsynphot/spectrum.py:615: AstropyUserWarning: Failed to load Vega spectrum from /tmp/trds/calspec/alpha_lyr_stis_010.fits; Functionality involving Vega will be cripped: FileNotFoundError(2, 'No such file or directory')
    warnings.warn(

/home/runner/work/stenv/stenv/stsynphot/conftest.py:16: AstropyDeprecationWarning: The enable_deprecations_as_exceptions function is deprecated and may be removed in a future version.
          Use https://docs.pytest.org/en/stable/warnings.html instead.
    enable_deprecations_as_exceptions()

[zacharyburnett]

the current workaround is to disable the tests in the workflow