[beatreceivers] fix race condition in beat LoadMeta

[leehinman]

Proposed commit message

Fix race condition in beat LoadMeta function. If 2 (or more) beats had the same path to the meta file, then it was possible for one not to start. This would only affect beat receivers because a normal beat requires a unique path to the meta file.

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
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

Author's Checklist

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How to test this PR locally

cd libbeat/cmd/instance
go test . -v -count 1 -run TestMultipleLoadMeta

Related issues

• Closes [beat] LoadMeta has a race condition. #46841

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[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b 46841_load_meta_race_condition upstream/46841_load_meta_race_condition
git merge upstream/main
git push upstream 46841_load_meta_race_condition

[elasticmachine]

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

[cmacknz]

Test fails if you go back to using just os.OpenFile so this fixes things as expected 👍