fix: runner not picking up jobs - bash syntax error and label contention

- Remove trailing & causing bash syntax error (& &&) in SANDBOX_CMD
- Add unique job-${{ github.run_id }} label to test.yml runs-on
  to prevent label contention between JIT runners

Author: manascb1344

.github/workflows/test.yml

@@ -6,7 +6,7 @@ on:
 
 jobs:
   test-modal-runner:
-    runs-on: [self-hosted, modal]
+    runs-on: [self-hosted, modal, "job-${{ github.run_id }}"]
     steps:
       - name: Hello World
         run: |

runner/services/sandbox_service.py

@@ -115,7 +115,7 @@ def build_runner_image() -> modal.Image:
 SANDBOX_CMD = (
     "bash -c '/start-dockerd.sh &'"
     " && for i in $(seq 1 10); do docker info > /dev/null 2>&1 && break; sleep 1; done"
-    " && (docker load -i /images/node-22-alpine.tar 2>/dev/null || true) &"
+    " && (docker load -i /images/node-22-alpine.tar 2>/dev/null || true)"
     " && cd /actions-runner"
     " && export RUNNER_ALLOW_RUNASROOT=1"
     " && export DOCKER_BUILDKIT=1"