Update astropy requirement from ~=5.3 to ~=6.0 (#114)

Updates the requirements on [astropy](https://github.com/astropy/astropy) to permit the latest version.
- [Release notes](https://github.com/astropy/astropy/releases)
- [Changelog](https://github.com/astropy/astropy/blob/main/docs/changelog.rst)
- [Commits](astropy/astropy@v5.3...v6.0.0)

---
updated-dependencies:
- dependency-name: astropy
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -3,7 +3,7 @@ dill~=0.3
 h5py~=3.10
 lmfit~=1.2
 cython~=3.0
-astropy~=5.3
+astropy~=6.0
 scipy~=1.11
 scikit-image~=0.22
 sep~=1.2

requirements_dev.txt

@@ -3,7 +3,7 @@ dill~=0.3
 h5py~=3.10
 lmfit~=1.2
 cython~=3.0
-astropy~=5.3
+astropy~=6.0
 scipy~=1.11
 scikit-image~=0.22
 sep~=1.2