TST: Change PIP_EXTRA_INDEX_URL

[pllim]

Description

Change PIP_EXTRA_INDEX_URL because packages moved where they upload nightly builds. This is one of the things they did at Scientific Python Developers Summit 2023.

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.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (dad1bd9) 91.59% compared to head (8169a6d) 91.59%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2231   +/-   ##
=======================================
  Coverage   91.59%   91.59%           
=======================================
  Files         148      148           
  Lines       16496    16496           
=======================================
  Hits        15110    15110           
  Misses       1386     1386           

Impacted Files	Coverage Δ
jdaviz/configs/cubeviz/helper.py	98.87% <ø> (ø)

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