ci(docker): use self-hosted arm64 builds

.github/workflows/ci.yml

@@ -42,9 +42,11 @@ jobs:
     strategy:
       matrix:
         platform: ${{ fromJSON(needs.platforms.outputs.platforms) }}
-    runs-on: ${{ contains(matrix.platform, '/arm') && 'macos-latest-xlarge' || 'ubuntu-latest' }}
+    # Run on our own self-hosted ARM64 machine if the platform is ARMish.
+    runs-on: ${{ contains(matrix.platform, '/arm') && fromJSON('["self-hosted","Linux","ARM64"]') || 'ubuntu-latest' }}
     steps:
       - name: free up disk space
+        if: ${{ !contains(matrix.platform, '/arm') }}
         run: |
           # Workaround to provide additional free space for testing.
           #   https://github.com/actions/runner-images/issues/2840#issuecomment-790492173
@@ -70,7 +72,6 @@ jobs:
 
       - name: Set up QEMU for cross-platform builds
         uses: docker/setup-qemu-action@v3
-        if: ${{ matrix.platform != env.DEFAULT_PLATFORM }}
 
       - name: Log in to the Container registry
         uses: docker/login-action@v3
@@ -87,7 +88,7 @@ jobs:
           images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
 
         # The .ts scripts depend upon this
-      - run: npm install --global tsx
+      - run: tsx --version || npm install --global tsx
 
       - name: build test images if ${{ matrix.platform }} == ${{ env.DEFAULT_PLATFORM }}
         run: |