GHA ubuntu.yml: remove ubuntu-24.04-arm for now

Author: msgilligan

.github/workflows/ubuntu.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-24.04, ubuntu-24.04-arm]
+        os: [ubuntu-24.04]
       fail-fast: false
     env:
       # HOST_ARCH value must match string in Lima download filename