test with specutils similar to NERSC version

.github/workflows/python-package.yml

@@ -78,7 +78,7 @@ jobs:
                 python -m pip install pytest pytest-cov coveralls
                 python -m pip install git+https://github.com/desihub/desiutil.git@${DESIUTIL_VERSION}#egg=desiutil
                 python -m pip install -r requirements.txt
-                ### python -m pip install specutils
+                python -m pip install specutils\<1.15
                 python -m pip install -U 'numpy${{ matrix.numpy-version }}'
                 python -m pip install -U 'astropy${{ matrix.astropy-version }}'
                 python -m pip cache remove fitsio