image-builder: pass --pull on docker build

One of the runners has a corrupted buildkit cache for the umoci layer
("/bin/sh: no such file or directory" mid-RUN). --pull refreshes the
ubuntu:24.04 base, which invalidates all downstream cached layers and
forces the umoci step to actually re-execute.

build_image.sh

@@ -355,7 +355,7 @@ fi
 
 # --- Step 2: Build distribution image ---
 run_stage "Build image builder image" \
-    docker build -t ps5-image-builder -f "$SCRIPT_DIR/docker/image-builder/Dockerfile" "$SCRIPT_DIR"
+    docker build --pull -t ps5-image-builder -f "$SCRIPT_DIR/docker/image-builder/Dockerfile" "$SCRIPT_DIR"
 
 if [ "$DISTRO" = "all" ]; then
     DOCKER_ARGS=(