TST: Fix specviz2d test failure

[pllim]

Description

I don't know why it increased to 15. I just want the green checkmark back.

Fixes #2476

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

Checklist for package maintainer(s)

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• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
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• Did the CI pass? If not, are the failures related?
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• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Patch coverage is 100.00% of modified lines.

Files Changed	Coverage
...ctral_extraction/tests/test_spectral_extraction.py	100.00%

📢 Thoughts on this report? Let us know!.

[kecnry]

We definitely need to track down what changed here. At the least we should add a check on the length before to make sure that the intention of the test of 3 new marks works, and then probably inspect the 12 marks before this to make sure nothing has been added (like an all-nan green layer...).

[pllim]

I haven't been following specviz2d development so I have no idea what is going on. And I cannot look at this more today. We can merge this to get green CI and open follow up ticket to debug next sprint?

[kecnry]

The extra mark that didn't used to be there seems to be a GenericDensityMark and only appears with glue-jupyter 0.19 (but not 0.18). I'm guessing this was introduced by glue-viz/glue-jupyter#398 (even though we aren't using a scatter viewer in specviz2d). @astrofrog - is this expected?

I'll try to reproduce in the app and see what the mark itself is and if its "harmful" or safe to ignore and update the test.

[kecnry]

The marks itself seems to be harmless - its not visible by default, and even when made visible and the only mark, doesn't actually show anything. So I say we can merge this for now to get CI green in other PRs, but we might want a follow-up ticket/issue to try to track down the cause upstream and revert this (maybe with an inline-comment in the test pointing to that, since otherwise 11+3=15 is going to confuse someone in the future).

[pllim]

maybe with an inline-comment in the test pointing to that

Added a comment. Is that sufficient?