Use astropy nightly build in devdeps Jenkins job

[nden]

The JWST Jenkins devdeps build is failing because astropy from master does not build. Following the example in spacetelescope/drizzlepac#1502 this uses the astropy nightly builds

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

Base: 77.90% // Head: 77.90% // No change to project coverage 👍

Coverage data is based on head (8a0a3ee) compared to base (fbe36f0).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7462   +/-   ##
=======================================
  Coverage   77.90%   77.90%           
=======================================
  Files         455      455           
  Lines       36975    36975           
=======================================
  Hits        28806    28806           
  Misses       8169     8169           

Flag	Coverage Δ		*Carryforward flag
nightly	77.89% <ø> (ø)		Carriedforward from fbe36f0
unit	50.43% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

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