Bump astropy from 5.2.1 to 5.3.3 in /extra_requirements

Bumps [astropy](https://github.com/astropy/astropy) from 5.2.1 to 5.3.3.
- [Release notes](https://github.com/astropy/astropy/releases)
- [Changelog](https://github.com/astropy/astropy/blob/main/docs/changelog.rst)
- [Commits](astropy/astropy@v5.2.1...v5.3.3)

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

Signed-off-by: dependabot[bot] <[email protected]>

extra_requirements/requirements-tests.txt

@@ -1,5 +1,5 @@
 astropy==4.3.1; python_version<='3.7'
-astropy==5.2.1; python_version>'3.7'
+astropy==5.3.3; python_version>'3.7'
 coverage==6.5.0
 coveralls==3.3.1
 galpy==1.8.3