Multi arch cpu (#746)

Encountered a similar problem as in
https://github.com/mostlygeek/llama-swap/issues/709 but in my case I
only needed the :cpu version.

So decided to add the github action to build arm64 combined with the
amd64 version on the same :cpu tag. Already tested it from this fork:
ghcr.io/rhtenhove/llama-swap:cpu and it works perfectly fine.

Adding GPU support is a whole other beast, needing quite a bit more work
and isn't something I can test.

.github/workflows/containers.yml

@@ -33,7 +33,7 @@ jobs:
       fail-fast: false
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Free up disk space
         if: matrix.platform == 'rocm'
@@ -48,8 +48,18 @@ jobs:
           echo "After cleanup:"
           df -h
 
+      # QEMU enables arm64 cross-builds on the amd64 GitHub runner.
+      # Currently only the cpu backend goes multi-arch; the action is a
+      # no-op for amd64-only builds, so leaving it on for every matrix
+      # entry keeps the workflow simple.
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v4
+
       - name: Log in to GitHub Container Registry
-        uses: docker/login-action@v2
+        uses: docker/login-action@v4
         with:
           registry: ghcr.io
           username: ${{ github.actor }}
@@ -64,6 +74,9 @@ jobs:
   # see: https://github.com/actions/delete-package-versions/issues/74
   delete-untagged-containers:
     needs: build-and-push
+    # Skip on forks — the delete API requires package-admin on the
+    # upstream account and would otherwise red-x every fork CI run.
+    if: github.repository == 'mostlygeek/llama-swap'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/delete-package-versions@v5