Increase astropy_healpix version to be compatible with astropy 6.0

[bhazelton]

Description

When I updated our minimum version requirements I missed that astropy_healpix needed to be updated to be compatible with astropy>=6.0. This didn't cause errors because the import failed so tests that needed astropy_healpix were just skipped in the min_versions CI. I didn't notice that there were a lot of skipped tests in that CI.

I also made pyyaml a required dependency because it's required by astropy.

Motivation and Context

Needed for dependency consistency.

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 change)
• Documentation change (documentation changes only)
• Version change
• Build or continuous integration change

Checklist:

• I have read the contribution guide.
• My code follows the code style of this project.

Build or continuous integration change checklist:

• If required or optional dependencies have changed (including version numbers), I have updated the readme to reflect this.
• If this is a new CI setup, I have added the associated badge to the readme and to references/make_index.py (if appropriate).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.92%. Comparing base (f9d0df7) to head (590aa7a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1423   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files          37       37           
  Lines       20871    20871           
=======================================
  Hits        20855    20855           
  Misses         16       16           

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[kartographer]

One minor error to fix...

[kartographer]

Looks good, thanks @bhazelton!