ci: Ensure binfmt is set up for arm64. Skip s390x

s390x emulation is broken. All emulated builds fail with.
Illegal Instruction and/or Segfaults.

Signed-off-by: Dave Tucker <dave@dtucker.co.uk>

.github/workflows/ci.yml

@@ -91,6 +91,10 @@ jobs:
       with:
         path: ./src/github.com/linuxkit/linuxkit
 
+    - name: Set up binfmt
+      # Only register arm64 as we are on amd64 already. s390x is not reliable
+      run: docker run --privileged --rm tonistiigi/binfmt --install arm64
+
     - name: Download linuxkit
       uses: actions/download-artifact@v2
       with:
@@ -112,8 +116,9 @@ jobs:
           ${{ runner.os }}-linuxkit-
 
     - name: Build Packages
+      # Skip s390x as emulation is unreliable
       run: |
-        make -C pkg build
+        make OPTIONS="--skip-platforms linux/s390x" -C pkg build
 
   test_packages:
     name: Packages Tests