Update astropy requirement to 5.0.4 to fix IERS issue, drop python 3.7 support

[bhazelton]

Description

• Update astropy requirement to 5.0.4 to fix an ongoing IERS problem (see datacenter.iers.org SSL: CERTIFICATE_VERIFY_FAILED (Column year failed to convert: invalid literal for int() with base 10: '<!') astropy/astropy#12998).
• As of 5.0, astropy dropped support for python 3.7, so this PR drops 3.7 and adds 3.10 testing.
• Change the MPI version test to check that the MPI version is greater than or equal to 3 rather than exactly 3.

Motivation and Context

Fix CI errors on other PRs related to IERS issues.
Also fixes #396

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)
• Reference simulation update or replacement
• Documentation change (documentation changes only)
• Version change
• Build or continuous integration change

Checklist:

For all pull requests:

• 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

Merging #397 (50c8ed1) into main (8092079) will decrease coverage by 0.61%.
The diff coverage is n/a.

❗ Current head 50c8ed1 differs from pull request most recent head c480c63. Consider uploading reports for the commit c480c63 to get more accurate results

@@            Coverage Diff             @@
##             main     #397      +/-   ##
==========================================
- Coverage   99.34%   98.73%   -0.62%     
==========================================
  Files          13       13              
  Lines        2126     2126              
==========================================
- Hits         2112     2099      -13     
- Misses         14       27      +13     

Impacted Files	Coverage Δ
pyuvsim/simsetup.py	98.63% <0.00%> (-1.26%)	⬇️
pyuvsim/mpi.py	99.48% <0.00%> (-0.52%)	⬇️

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[mkolopanis]

This looks good to me. Astropy always forcing us to update our dependencies