Enable aarch64-linux build job

Re-enable the aarch64-linux build job in GitHub Actions.

Author: angerman

.github/workflows/aarch64-linux.yml

@@ -5,7 +5,6 @@ on:
 
 jobs:
   build:
-    if: false  # Disabled until we have a new aarch64-linux hydra builder
     name: Prebuild and Upload
     uses: ./.github/workflows/main.yml
     with: