Fix intersphinx linking

[mkelley]

from sphinx_astropy.conf.v1 import * was mistakenly deleted in #427 . But while I'm here, add a few more packages for intersphinx linking: numpy, scipy, matplotlib

[github-actions]

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[mkelley]

No change log entry needed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.81%. Comparing base (59a8a49) to head (92346cd).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #449   +/-   ##
=======================================
  Coverage   81.81%   81.81%           
=======================================
  Files          53       53           
  Lines        4267     4267           
=======================================
  Hits         3491     3491           
  Misses        776      776           

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