BLD: Set astropy oldest supported version to 4.3 (#645)

tox.ini

@@ -3,7 +3,7 @@ envlist =
     py{39,310,311,312,313}-test{,-all}{,-dev,-latest,-oldest}{,-cov}
     py{39,310,311,312,313}-test-numpy{119,120,121,122,123,124,125,126,20,21,22}
     py{39,310,311,312,313}-test-scipy{16,17,18,19,110,111,112,113,114,115}
-    py{39,310,311,312,313}-test-astropy{40,41,42,43,50,51,52,53,60,61,70}
+    py{39,310,311,312,313}-test-astropy{43,50,51,52,53,60,61,70}
     build_docs
     linkcheck
     codestyle
@@ -57,9 +57,6 @@ description =
     scipy113: with scipy 1.13.*
     scipy114: with scipy 1.14.*
     scipy114: with scipy 1.15.*
-    astropy40: with astropy 4.0.*
-    astropy41: with astropy 4.1.*
-    astropy42: with astropy 4.2.*
     astropy43: with astropy 4.3.*
     astropy50: with astropy 5.0.*
     astropy51: with astropy 5.1.*
@@ -95,9 +92,6 @@ deps =
     scipy114: scipy==1.14.*
     scipy114: scipy==1.15.*
 
-    astropy40: astropy==4.0.*
-    astropy41: astropy==4.1.*
-    astropy42: astropy==4.2.*
     astropy43: astropy==4.3.*
     astropy50: astropy==5.0.*
     astropy51: astropy==5.1.*
@@ -115,7 +109,7 @@ deps =
     latest: numpy==2.2.*
     latest: scipy==1.15.*
 
-    oldest: astropy==4.0.*
+    oldest: astropy==4.3.*
     oldest: numpy==1.19.*
     oldest: scipy==1.6.*