ci: bump docker builder rust toolchain

docker/client.Dockerfile

@@ -1,4 +1,4 @@
-FROM rust:1.87-bookworm AS builder
+FROM rust:1.88-bookworm AS builder
 
 WORKDIR /src
 

docker/server.Dockerfile

@@ -1,4 +1,4 @@
-FROM rust:1.87-bookworm AS builder
+FROM rust:1.88-bookworm AS builder
 
 WORKDIR /src
 

scripts/ci/build-images.sh

@@ -18,18 +18,24 @@ should_push() {
 build_with_buildx() {
   local dockerfile=$1
   local image=$2
+  local platform_args=()
 
   if should_push; then
+    platform_args=(--platform "${PLATFORMS}")
     docker buildx build \
-      --platform "${PLATFORMS}" \
+      "${platform_args[@]}" \
       -f "${dockerfile}" \
       -t "${image}:${IMAGE_TAG}" \
       -t "${image}:latest" \
       --push \
       "${ROOT_DIR}"
   else
+    # buildx cannot `--load` a manifest list, so load the host platform only.
+    local host_platform
+    host_platform="$(docker version --format '{{.Server.Os}}/{{.Server.Arch}}' 2>/dev/null || echo linux/amd64)"
+    platform_args=(--platform "${host_platform}")
     docker buildx build \
-      --platform "${PLATFORMS}" \
+      "${platform_args[@]}" \
       -f "${dockerfile}" \
       -t "${image}:${IMAGE_TAG}" \
       -t "${image}:latest" \