Unpin astropy version

[epassaro]

Description

Change astropy required version from tardis_env3.yml

Motivation and Context

astropy was pinned strictly to v3.2.1 after accidentally merging #995.

How Has This Been Tested?

All test pass.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have assigned/requested two reviewers for this pull request.

[codecov]

Codecov Report

Merging #1193 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1193   +/-   ##
=======================================
  Coverage   77.13%   77.13%           
=======================================
  Files          89       89           
  Lines        5551     5551           
=======================================
  Hits         4282     4282           
  Misses       1269     1269           

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[Rodot-]

This looks good and doesn't seem to break anything at the moment.