Fix multi-platform Docker build failures in CI

Remove BuildKit cache mounts from pixi-installer stage to resolve QEMU
emulation issues when building ARM64 images on AMD64 runners. The cache
mounts cause apt-get operations to fail with exit code 100 in emulated
environments.

Also remove unused BASE_IMAGE build argument from CI workflow since the
hardened Dockerfile now uses digest-pinned base images.

Changes:
- Remove --mount=type=cache flags from pixi-installer stage
- Remove BASE_IMAGE and GPU_BASE_IMAGE env vars from workflow
- Remove build-args: BASE_IMAGE from build step

Author: dcmcand

.github/workflows/build-push-docker.yaml

@@ -27,9 +27,7 @@ on:
 
 env:
   DOCKER_ORG: nebari
-  GPU_BASE_IMAGE: nvidia/cuda:12.2.2-base-ubuntu20.04
   GPU_IMAGE_SUFFIX: gpu
-  BASE_IMAGE: ubuntu:20.04
 
 permissions:
   contents: read
@@ -85,11 +83,10 @@ jobs:
           username: ${{ secrets.QUAY_USERNAME }}
           password: ${{ secrets.QUAY_TOKEN }}
 
-      - name: "Set BASE_IMAGE and Image Suffix 📷"
+      - name: "Set Image Suffix 📷"
         if: ${{ matrix.platform == 'gpu' }}
         run: |
           echo "GPU Platform Matrix"
-          echo "BASE_IMAGE=$GPU_BASE_IMAGE" >> $GITHUB_ENV
           echo "IMAGE_SUFFIX=-$GPU_IMAGE_SUFFIX" >> $GITHUB_ENV
 
       - name: "Generate Docker images tags 🏷️"
@@ -123,7 +120,6 @@ jobs:
           labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=gha
           cache-to: type=gha,mode=max
-          build-args: BASE_IMAGE=${{ env.BASE_IMAGE }}
           platforms: linux/amd64,linux/arm64
           sbom: true
           provenance: true

Dockerfile

@@ -22,9 +22,7 @@ ARG PIXI_VERSION
 ARG PIXI_AMD64_SHA256
 ARG PIXI_ARM64_SHA256
 
-RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,target=/var/lib/apt,sharing=locked \
-    apt-get update && apt-get install -y --no-install-recommends \
+RUN apt-get update && apt-get install -y --no-install-recommends \
     wget \
     ca-certificates && \
     ARCH=$(dpkg --print-architecture) && \