client+server/docker: fix ARM build platform issue

.github/workflows/build-containers.yml

@@ -42,7 +42,7 @@ jobs:
       - name: Build container
         run: >
           docker buildx build --push
-          --platform linux/amd64,linux/arm64,linux/arm/v7,linux/arm/v6
+          --platform linux/amd64,linux/arm/v7,linux/arm64/v8
           --build-arg BUILD_INFO=${{ env.build_info }}
           --build-arg BUILD_DATE=${{ env.build_date }}
           --build-arg SOURCE_COMMIT=$GITHUB_SHA
@@ -93,7 +93,7 @@ jobs:
       - name: Build container
         run: >
           docker buildx build --push
-          --platform linux/amd64,linux/arm64,linux/arm/v7,linux/arm/v6
+          --platform linux/amd64,linux/arm/v7,linux/arm64/v8
           --build-arg BUILD_DATE=${{ env.build_date }}
           --build-arg SOURCE_COMMIT=$GITHUB_SHA
           --build-arg DOCKER_REPO=szurubooru/server

client/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:lts as builder
+FROM --platform=$BUILDPLATFORM node:lts as builder
 WORKDIR /opt/app
 
 COPY package.json package-lock.json ./
@@ -12,7 +12,7 @@ ARG CLIENT_BUILD_ARGS=""
 RUN BASE_URL="__BASEURL__" node build.js --gzip ${CLIENT_BUILD_ARGS}
 
 
-FROM scratch as approot
+FROM --platform=$BUILDPLATFORM scratch as approot
 
 COPY docker-start.sh /
 

server/Dockerfile

@@ -37,7 +37,7 @@ COPY ./ /opt/app/
 RUN rm -rf /opt/app/szurubooru/tests
 
 
-FROM prereqs as testing
+FROM --platform=$BUILDPLATFORM prereqs as testing
 WORKDIR /opt/app
 
 RUN apk --no-cache add \