ci: run tests on GitHub-hosted ubuntu-24.04-arm instead of self-hosted arcp runners

Decommissioning the spruce-hosted arcp self-hosted runner pool. ubuntu-24.04-arm
keeps the arm64 test architecture and is free for public repos.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: nficano

.github/workflows/test.yml

@@ -37,7 +37,7 @@ permissions:
 jobs:
   test:
     name: test (${{ matrix.tfm }})
-    runs-on: [self-hosted, linux, arm64, arcp]
+    runs-on: ubuntu-24.04-arm
     strategy:
       fail-fast: false
       matrix: