Use different machines for linux arm64 (#21099)

.azure/pipelines/ci.yml

@@ -492,6 +492,7 @@ stages:
       jobName: Linux_musl_arm64_build
       jobDisplayName: "Build: Linux Musl ARM64"
       agentOs: Linux
+      useHostedUbuntu: false
       buildScript: ./dockerbuild.sh ubuntu-alpine37
       buildArgs:
         --ci