fix telemetry test

[juliaElastic]

Closes #156245

One test agent went from offline to inactive due to inactivity timeout and broke the tests, instead changed the last_checkin to now-6m so it stays in offline state.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[ghost]

🤖 GitHub comments

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Just comment with:

• /oblt-deploy : Deploy a Kibana instance using the Observability test environments.
• /oblt-deploy-serverless : Deploy a serverless Kibana instance using the Observability test environments.
• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: f2e4a2f

Failed CI Steps

• FTR Configs #22
• Osquery Cypress Tests #2

Test Failures

• [job] [logs] FTR Configs #22 / serverless search UI persistable attachment "before all" hook in "persistable attachment"

Metrics [docs]

✅ unchanged

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @juliaElastic