CI: add arm64 builds to nighly

Author: junghans

.github/workflows/Nightly.yml

@@ -18,7 +18,11 @@ jobs:
       matrix:
         backend: ["OPENMP", "SERIAL"]
         distro: ['ubuntu:latest', 'fedora:rawhide']
-    runs-on: ubuntu-20.04
+        include:
+          - distro: 'ubuntu:latest'
+            backend: 'THREADS'
+            arch: 'arm64'
+    runs-on: ${{ matrix.config.arch == 'arm64' && 'ubuntu-24.04-arm' || 'ubuntu-latest' }}
     timeout-minutes: 30
     container:
       image: ghcr.io/ecp-copa/ci-containers/${{ matrix.distro }}