Change ARM64 build runner from Ubuntu to macOS

ACL2 complains about the lack of expected FP trap handling on ubuntu-arm so let's try macos-latest, that's what works for me on my Mac Studio.

Author: jimwhite

.github/workflows/docker-release.yml

@@ -100,7 +100,7 @@ jobs:
   # Build ARM64 image on native arm64 runner
   build-arm64:
     needs: prepare
-    runs-on: ubuntu-24.04-arm
+    runs-on: macos-latest
     permissions:
       contents: read
       packages: write