bump builder image for the Knots versions where it can be done

.github/workflows/build.yml

@@ -13,11 +13,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        knots-version:
-          - 27.1.knots20240621
-          - 26.1.knots20240513
-          - 26.1.knots20240325
-          - 25.1.knots20231115
+        versions:
+          - { knots: "27.1.knots20240621", alpine-builder: "3.20" }
+          - { knots: "26.1.knots20240513", alpine-builder: "3.20" }
+          - { knots: "26.1.knots20240325", alpine-builder: "3.18" }
+          - { knots: "25.1.knots20231115", alpine-builder: "3.18" }
     steps:
       - uses: actions/checkout@v4
       - uses: docker/setup-qemu-action@v3
@@ -29,7 +29,8 @@ jobs:
       - uses: docker/build-push-action@v5
         with:
           build-args: |
-            KNOTS_VERSION=${{ matrix.knots-version }}
+            KNOTS_VERSION=${{ matrix.versions.knots }}
+            ALPINE_BUILDER_VERSION=${{ matrix.alpine-builder }}
           cache-from: type=registry,ref=1maa/bitcoin:v${{ matrix.knots-version }}
           cache-to: type=inline
           context: .

Dockerfile

@@ -1,5 +1,6 @@
 FROM alpine:3.20 AS verifier
 
+ARG ALPINE_BUILDER_VERSION
 ARG KNOTS_VERSION
 
 WORKDIR /tmp
@@ -20,7 +21,7 @@ RUN apk add --no-cache \
  && sha256sum --ignore-missing -c SHA256SUMS
 
 
-FROM alpine:3.18 AS builder
+FROM alpine:${ALPINE_BUILDER_VERSION} AS builder
 
 ARG KNOTS_VERSION