Add alpine 3.21

https://alpinelinux.org/posts/Alpine-3.21.0-released.html

As customary, drop alpine 3.19

Author: Earlopain

3.1/alpine3.19/Dockerfile 3.1/alpine3.21/Dockerfile3.1/alpine3.19/Dockerfile renamed to 3.1/alpine3.21/Dockerfile

@@ -33,8 +33,8 @@
       "slim-bookworm",
       "bullseye",
       "slim-bullseye",
-      "alpine3.20",
-      "alpine3.19"
+      "alpine3.21",
+      "alpine3.20"
     ]
   },
   "3.2": {
@@ -71,8 +71,8 @@
       "slim-bookworm",
       "bullseye",
       "slim-bullseye",
-      "alpine3.20",
-      "alpine3.19"
+      "alpine3.21",
+      "alpine3.20"
     ],
     "rust": {
       "version": "1.74.1"
@@ -141,8 +141,8 @@
       "slim-bookworm",
       "bullseye",
       "slim-bullseye",
-      "alpine3.20",
-      "alpine3.19"
+      "alpine3.21",
+      "alpine3.20"
     ],
     "rust": {
       "version": "1.74.1"
@@ -218,8 +218,8 @@
       "slim-bookworm",
       "bullseye",
       "slim-bullseye",
-      "alpine3.20",
-      "alpine3.19"
+      "alpine3.21",
+      "alpine3.20"
     ],
     "rust": {
       "version": "1.74.1"

3.2/alpine3.19/Dockerfile 3.2/alpine3.21/Dockerfile3.2/alpine3.19/Dockerfile renamed to 3.2/alpine3.21/Dockerfile

@@ -88,8 +88,8 @@ for version in "${versions[@]}"; do
 				empty # trailing comma hack
 			| ., "slim-" + .), # https://github.com/docker-library/ruby/pull/142#issuecomment-320012893
 			(
+				"3.21",
 				"3.20",
-				"3.19",
 				empty # trailing comma hack
 			| "alpine" + .)
 		]