Support Alpine 3.21 (#1277)

* Alpine upgraed to version 3.21

* Update README.md to resolve conflict

* Update README.md to add reference of Alpine 3.21

Author: Kaniska244

src/base-alpine/.devcontainer/Dockerfile

@@ -1,2 +1,2 @@
-ARG VARIANT=3.20
+ARG VARIANT=3.21
 FROM alpine:${VARIANT}

src/base-alpine/README.md

@@ -9,7 +9,7 @@
 | *Categories* | Core, Other |
 | *Image type* | Dockerfile |
 | *Published images* | mcr.microsoft.com/devcontainers/base:alpine |
-| *Available image variants* | alpine-3.20, alpine-3.19, alpine-3.18 ([full list](https://mcr.microsoft.com/v2/devcontainers/base/tags/list)) |
+| *Available image variants* | alpine-3.21, alpine-3.20, alpine-3.19, alpine-3.18 ([full list](https://mcr.microsoft.com/v2/devcontainers/base/tags/list)) |
 | *Published image architecture(s)* | x86-64, aarch64/arm64 |
 | *Container host OS support* | Linux, macOS, Windows |
 | *Container OS* | Alpine Linux |
@@ -22,6 +22,7 @@ See **[history](history)** for information on the contents of published images.
 You can also directly reference pre-built versions of `.devcontainer/Dockerfile` by using the `image` property in `.devcontainer/devcontainer.json` or updating the `FROM` statement in your own  `Dockerfile` to one of the following. An example `Dockerfile` is included in this repository.
 
 - `mcr.microsoft.com/devcontainers/base:alpine` (latest)
+- `mcr.microsoft.com/devcontainers/base:alpine-3.21`
 - `mcr.microsoft.com/devcontainers/base:alpine-3.20`
 - `mcr.microsoft.com/devcontainers/base:alpine-3.19`
 - `mcr.microsoft.com/devcontainers/base:alpine-3.18`

src/base-alpine/manifest.json

@@ -1,6 +1,7 @@
 {
 	"version": "0.209.7",
 	"variants": [
+		"3.21",		
 		"3.20",
 		"3.19",
 		"3.18"
@@ -17,7 +18,7 @@
 			"base:${VERSION}-alpine${VARIANT}"
 		],
 		"variantTags": {
-			"3.20": [
+			"3.21": [
 				"base:${VERSION}-alpine"
 			]
 		}