JP-3469: Replace nanmedian with masked array median in ifu_autocen

[drlaw1558]

Resolves JP-3469 by replacing a nanmedian calculation with a numpy masked median calculation.

Checklist for maintainers

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• Make sure the JIRA ticket is resolved properly

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (5b63bda) 75.95% compared to head (a4759ef) 75.95%.
Report is 1 commits behind head on master.

❗ Current head a4759ef differs from pull request most recent head e6292a6. Consider uploading reports for the commit e6292a6 to get more accurate results

Files	Patch %	Lines
jwst/extract_1d/ifu.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8080   +/-   ##
=======================================
  Coverage   75.95%   75.95%           
=======================================
  Files         459      459           
  Lines       37597    37597           
=======================================
  Hits        28557    28557           
  Misses       9040     9040           

Flag	Coverage Δ		*Carryforward flag
nightly	77.37% <ø> (ø)		Carriedforward from 5b63bda

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[hbushouse]

Started a regtest run at https://plwishmaster.stsci.edu:8081/job/RT/job/JWST/2661

[hbushouse]

Regtest run was clean (unrelated failures)