TST: Remote data job has 5 failures with HTTP Error 503

[pllim]

https://das.sdss.org/spectro/1d_26/0273/1d/spSpec-51957-0273-016.fit now throws 503 Service Unavailable. Need to find new data for these tests or rewrite them to not require remote data.

• specutils/tests/test_loaders.py::test_sdss_spspec
• specutils/tests/test_loaders.py::test_sdss_spspec_stream
• specutils/tests/test_loaders.py::test_sdss_compressed[gzip]
• specutils/tests/test_loaders.py::test_sdss_compressed[bzip2]
• specutils/tests/test_loaders.py::test_sdss_compressed[xz]