[9.2] (backport #11285) chore: add changelog entry for a bugfix in elastic-agent-system-metrics v0.13.4

[mergify]

What does this PR do?

See title.

See release notes for elastic-agent-system-metrics v0.13.4 https://github.com/elastic/elastic-agent-system-metrics/releases/tag/v0.13.4.

Checklist

• I have read and understood the pull request guidelines of this project.
• 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
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Related issues

• Closes [beats receivers] OTel manager failed: error creating metricbeatreceiver: error setting up metrics report: failed to init process stats for agent: failed to compile regexp [User.Name��]: error parsing regexp: invalid UTF-8: �� #11172

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  This is an automatic backport of pull request chore: add changelog entry for a bugfix in elastic-agent-system-metrics v0.13.4 #11285 done by Mergify.

[elasticmachine]

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