[8.19](backport #48830) Update elastic-agent-system-metrics to fix #48690

[mergify]

Proposed commit message

See title

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works. Where relevant, I have used the stresstest.sh script to run them under stress conditions and race detector to verify their stability.
• I have added an entry in ./changelog/fragments using the changelog tool.

## Disruptive User Impact
## Author's Checklist

How to test this PR locally

The reproduction steps are a modified version of #48690. Here the discard output is used.

cat <<'EOF' > repro.yml
logging.level: error
metricbeat.modules:
- module: system
  metricsets: ["cpu"]
  hostfs: "/hostfs"
  period: 10s
output.discard:
    enabled: true
EOF

docker run --rm \
  --name=metricbeat \
  --volume="$(pwd)/repro.yml:/usr/share/metricbeat/metricbeat.yml:ro" \
  --volume="/var/run/docker.sock:/var/run/docker.sock:ro" \
  --volume="/sys/fs/cgroup:/hostfs/sys/fs/cgroup:ro" \
  --volume="/proc:/hostfs/proc:ro" \
  --volume="/:/hostfs:ro" \
  docker.elastic.co/beats/metricbeat:9.3.0 metricbeat -e

Because the log level is set to error in the configuration file and this PR fixes the error, there will be no logs.

Related issues

• Metricbeat container throws errors when fetching metrics with hostfs set #48690

## Use cases
## Screenshots
## Logs

---

This is an automatic backport of pull request #48830 done by [Mergify](https://mergify.com).

[mergify]

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[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[mergify]

This pull request has not been merged yet. Could you please review and merge it @belimawr? 🙏