fix typo from PR 3159

[kecnry]

Description

This pull request fixes a typo introduced in #3159 causing the spectral extraction UI in cubeviz to fail to render.

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)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• 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?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone. Bugfix milestone also needs an accompanying backport label.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[rosteen]

I'll trust you on this one (although maybe I shouldn't! 😆 )

[kecnry]

Clearly not, that's how we got here in the first place! 😜

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.20%. Comparing base (0c63463) to head (a0319b6).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3165      +/-   ##
==========================================
- Coverage   87.20%   87.20%   -0.01%     
==========================================
  Files         121      121              
  Lines       18239    18239              
==========================================
- Hits        15906    15905       -1     
- Misses       2333     2334       +1     

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