Re-enable macOS and Linux platforms in workflow

Author: angerman

.github/workflows/hello.yml

@@ -12,11 +12,9 @@ jobs:
       matrix:
         platform:
           - x86_64-linux
-          # Disabled until macOS hydra builders are back online.
-          #- x86_64-darwin
-          # Skipping because we do not have runners for these set up.
-          #- aarch64-darwin
-          #- aarch64-linux
+          - x86_64-darwin
+          - aarch64-darwin
+          - aarch64-linux
         compiler-nix-name:
           - ghc96
           - ghc98