test(integration): de-flake otel pre-job config test

[cbartz]

What this PR does

De-flakes test_otel_collector_endpoint_pre_job_installs_config. Instead of dispatching a quick workflow, waiting for it to complete, then SSHing into the runner, it now dispatches the long-running wait workflow and inspects the runner while its job is in progress. The config read is polled to absorb the timing of the pre-job hook write.

Why we need it

The runner is ephemeral, so its OpenStack VM is torn down on job completion. Reading the otel config after completion races the runner-manager cleanup loop — when cleanup wins, get_single_runner finds zero VMs and the test fails with found more than one runners or no runners: []. This was observed failing on the 22.04 base while passing on 24.04 in the same run (e.g. PR #802 CI). Keeping the job in progress guarantees the VM is alive during inspection.

Checklist

• I followed the contributing guide
• I added or updated the documentation (if applicable) — N/A, test-only change
• I updated docs/changelog.md with user-relevant changes — N/A, no user-facing change
• I used AI to assist with preparing this PR
• I added or updated tests as needed (unit and integration)
• If this is a Grafana dashboard: I added a screenshot of the dashboard — N/A
• If this is Terraform: terraform fmt passes and tflint reports no errors — N/A
• If the github-runner-manager application has been changed: version updated in github-runner-manager/pyproject.toml — N/A, not changed