Move to Core-Eng build agents

- should resolve problems w/ disk space in "Tests: Helix ARM64 matrix" job
- need `node` in this job for some reason

Author: dougbu

.azure/pipelines/helix-matrix.yml

@@ -58,6 +58,7 @@ jobs:
       jobDisplayName: "Tests: Helix ARM64 matrix"
       agentOs: Linux
       timeoutInMinutes: 480
+      useHostedUbuntu: false
       steps:
       - script: ./eng/build.sh --ci --nobl --pack --arch arm64
                 /p:CrossgenOutput=false /p:ASPNETCORE_TEST_LOG_DIR=artifacts/log
@@ -69,7 +70,7 @@ jobs:
         env:
           HelixApiAccessToken: $(HelixApiAccessToken) # Needed for internal queues
           SYSTEM_ACCESSTOKEN: $(System.AccessToken) # We need to set this env var to publish helix results to Azure Dev Ops
-      installNodeJs: false
+      installNodeJs: true
       artifacts:
       - name: Helix_arm64_logs
         path: artifacts/log/