Attempt to reduce code reuse in action

Signed-off-by: Adam Warner <me@adamwarner.co.uk>

.github/workflows/v6-alpine-play.yml

@@ -16,19 +16,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
+        platform: [linux/amd64, linux/386, linux/arm/v6, linux/arm/v7, linux/arm64/v8]
+        container: [3.18]
         include:
-          - platform: linux/amd64
-            container: alpine:3.18
-          - platform: linux/386
-            container: alpine:3.18
-          - platform: linux/arm/v6
-            container: alpine:3.18
-          - platform: linux/arm/v7
-            container: alpine:3.18
-          - platform: linux/arm64/v8
-            container: alpine:3.18
           - platform: linux/riscv64
-            container: alpine:edge
+            container: edge
     steps:
       - name: Checkout Repo
         uses: actions/checkout@v3

src/Dockerfile

@@ -1,5 +1,5 @@
-ARG CONTAINER="alpine:edge"
-FROM ${CONTAINER}
+ARG CONTAINER="3.18"
+FROM alpine:${CONTAINER}
 # https://docs.docker.com/engine/reference/builder/#automatic-platform-args-in-the-global-scope
 ARG TARGETPLATFORM