Bump JarvusInnovations/background-action to v2

[sneridagh]

Bumps JarvusInnovations/background-action from v1 to v2 in the frontend-acceptance.yml shared workflow.

v2 notes relevant to our usage:

• Input values are now validated strictly. All values we use (tail: true, log-output: stderr,stdout, log-output-resume: stderr, log-output-if: failure, wait-for: 10m) are valid.
• Backgrounded servers are now stopped (SIGTERM) during post-run, after the acceptance tests have finished.
• Logs are written under RUNNER_TEMP instead of the workspace.
• Runs on the node24 runtime.

🤖 Generated with Claude Code

[sneridagh]

@ericof merging right away.