BLD: Set astropy latest supported version to 6.0 (#611)

tox.ini

@@ -3,7 +3,7 @@ envlist =
     py{37,38,39,310,311}-test{,-all}{,-dev,-latest,-oldest}{,-cov}
     py{37,38,39,310,311}-test-numpy{116,117,118,119,120,121,122,123,124,125,126}
     py{37,38,39,310,311}-test-scipy{12,13,14,15,16,17,18,19,110,111}
-    py{37,38,39,310,311}-test-astropy{40,41,42,43,50,51,52,53}
+    py{37,38,39,310,311}-test-astropy{40,41,42,43,50,51,52,53,60}
     build_docs
     linkcheck
     codestyle
@@ -65,6 +65,7 @@ description =
     astropy51: with astropy 5.1.*
     astropy52: with astropy 5.2.*
     astropy53: with astropy 5.3.*
+    astropy60: with astropy 6.0.*
 
 # The following provides some specific pinnings for key packages
 deps =
@@ -100,12 +101,13 @@ deps =
     astropy51: astropy==5.1.*
     astropy52: astropy==5.2.*
     astropy53: astropy==5.3.*
+    astropy60: astropy==6.0.*
 
     dev: numpy
     dev: scipy
     dev: git+https://github.com/astropy/astropy.git#egg=astropy
 
-    latest: astropy==5.3.*
+    latest: astropy==6.0.*
     latest: numpy==1.26.*
     latest: scipy==1.11.*