BUG: Fix HeI-HeII data file

[pllim]

Description

This pull request is to add a missing comma to the CSV data file.

Fixes #1430

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 change log needed? If yes, is it added to CHANGES.rst?
• Is a milestone set?
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Merging #1431 (1744617) into main (a1d7d83) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1431      +/-   ##
==========================================
+ Coverage   85.14%   85.15%   +0.01%     
==========================================
  Files          91       91              
  Lines        8325     8331       +6     
==========================================
+ Hits         7088     7094       +6     
  Misses       1237     1237              

Impacted Files	Coverage Δ
jdaviz/app.py	92.86% <0.00%> (ø)
jdaviz/core/template_mixin.py	91.42% <0.00%> (+0.07%)	⬆️

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[kecnry]

simple enough, thanks!