Update astropy requirement from ~=6.0 to ~=6.1

[dependabot[bot]]

Updates the requirements on astropy to permit the latest version.

Release notes

Sourced from astropy's releases.

v6.1.0

See https://docs.astropy.org/en/v6.1.0/changelog.html

Commits

• e97756f Merge pull request #16381 from astrofrog/v6.1.0-changelog
• 514bb02 Finalizing changelog for v6.1.0
• e3b482c Updated contributor statistics and names
• 4577b20 Merge pull request #16378 from meeseeksmachine/auto-backport-of-pr-16363-on-v...
• 523b0ed Backport PR #16363: UX: improved error message when instantiating a fits tabl...
• 0c92ffc Merge pull request #16373 from meeseeksmachine/auto-backport-of-pr-16368-on-v...
• b6d62d0 Backport PR #16368: Update minimum required version of astropy-iers-data
• c69b5f5 Merge pull request #16359 from meeseeksmachine/auto-backport-of-pr-16358-on-v...
• 44e3a43 Backport PR #16358: Pass character_as_bytes when converting Table to BinTableHDU
• c8016b4 Merge pull request #16350 from meeseeksmachine/auto-backport-of-pr-16348-on-v...
• Additional commits viewable in compare view

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[jmbhughes]

Can't accept until we require Python 3.10

[dependabot[bot]]

Looks like astropy is up-to-date now, so this is no longer needed.