feat(Dependencies): Update alpine Docker tag to v3.21.0

| datasource | package | from   | to     |
| ---------- | ------- | ------ | ------ |
| docker     | alpine  | 3.20.3 | 3.21.0 |

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.20.3
+FROM alpine:3.21.0
 ARG DEBIAN_FRONTEND=noninteractive
 
 RUN apk add --update --no-cache \