Handle GWCS for specutils 2.0 compatibility #137

Job	Run time
initial_checks / Load tox environments	8s
initial_checks / codestyle (ubuntu-latest)	16s
tests / Load tox environments	8s
tests / py38-test (ubuntu-latest)	1m 16s
tests / py39-test (ubuntu-latest)	1m 16s
tests / py310-test-dev (ubuntu-latest)	3m 26s
tests / py311-test-dev (ubuntu-latest)	2m 56s
tests / py311-test (macos-latest)	2m 11s
tests / py38-test (windows-latest)	2m 18s
tests / py39-test-dev (windows-latest)	3m 59s
tests / py310-test-dev (macos-latest)	9m 10s
publish	0s
	27m 4s

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