fix webbpsf data download cache

[braingram]

Similar to spacetelescope/romancal#1619

This won't work until:

• it's merged
• the cache is regenerated (by running https://github.com/spacetelescope/romanisim/actions/workflows/data.yml)

This is a stop-gap fix until this package can be migrated to stpsf.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.36%. Comparing base (244858c) to head (43d030a).
Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #203      +/-   ##
==========================================
- Coverage   90.02%   80.36%   -9.66%     
==========================================
  Files          17       17              
  Lines        2165     2175      +10     
==========================================
- Hits         1949     1748     -201     
- Misses        216      427     +211     

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[braingram]

Thanks! I don't have permissions to trigger the workflow at:
https://github.com/spacetelescope/romanisim/actions/workflows/data.yml
There should be a button to "Run workflow" (all defaults are fine)