BLD: Set numpy oldest supported version to 1.21 (#658)

Author: rrjbca

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 envlist =
     py{39,310,311,312,313}-test{,-all}{,-dev,-latest,-oldest}{,-cov}
-    py{39,310,311,312,313}-test-numpy{119,120,121,122,123,124,125,126,20,21,22,23,24}
+    py{39,310,311,312,313}-test-numpy{121,122,123,124,125,126,20,21,22,23,24}
     py{39,310,311,312,313}-test-scipy{16,17,18,19,110,111,112,113,114,115,116,117}
     py{39,310,311,312,313}-test-astropy{43,50,51,52,53,60,61,70,71,72}
     build_docs
@@ -36,8 +36,6 @@ description =
     latest: with the latest supported version of key dependencies
     oldest: with the oldest supported version of key dependencies
     cov: and test coverage
-    numpy119: with numpy 1.19.*
-    numpy120: with numpy 1.20.*
     numpy121: with numpy 1.21.*
     numpy122: with numpy 1.22.*
     numpy123: with numpy 1.23.*
@@ -75,8 +73,6 @@ description =
 # The following provides some specific pinnings for key packages
 deps =
 
-    numpy119: numpy==1.19.*
-    numpy120: numpy==1.20.*
     numpy121: numpy==1.21.*
     numpy122: numpy==1.22.*
     numpy123: numpy==1.23.*
@@ -122,7 +118,7 @@ deps =
     latest: scipy==1.17.*
 
     oldest: astropy==4.3.*
-    oldest: numpy==1.19.*
+    oldest: numpy==1.21.*
     oldest: scipy==1.6.*
 
 # The following indicates which extras_require from setup.cfg will be installed