[8.19](backport #47828) Fix flaky test TestFilestreamDelete

[mergify]

Proposed commit message

The two log messages are logged from different goroutines that race:

• "Closing reader of filestream" is logged from a background goroutine spawned by ctxtool.WithFunc when streamCancel() triggers cancellation
• "Stopped harvester for file" is logged from the main harvester goroutine via a defer in harvester.go

When streamCancel() executes, it closes a channel that wakes the background goroutine to log "Closing reader", while the main goroutine continues and logs "Stopped harvester". These two goroutines race to write to the log file, making the order non-deterministic.

The original test used sequential WaitLogsContains calls which track file offset - when messages appeared in the "wrong" order, the first check would advance the offset past both messages, causing the second to fail.

Changed to WaitLogsContainsAnyOrder which checks for both messages without relying on order.

Closes #47784

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.

How to test this PR locally

1. Start the integration test containers:

   cd filebeat && mage docker:composeUp

2. Build the test binary:

   mage buildSystemTestBinary

3. Run the specific test with FIPS mode (reproduces original failure without fix):

   GODEBUG=fips140=only \
   ES_HOST=localhost ES_USER=beats ES_PASS=testing \
   ES_SUPERUSER_USER=admin ES_SUPERUSER_PASS=testing \
   go test -v -failfast -tags "integration,requirefips" \
     -run "TestFilestreamDelete/Inactive_resource_not_finished_and_data_added_during_grace_period" \
     ./tests/integration/ -count=20

4. Clean up:

   mage docker:composeDown

Related issues

• Closes Flaky test: TestFilestreamDelete/Inactive_resource_not_finished_and_data_added_during_grace_period/grace_period_is_interrupted_when_file_changes #47784

  ---

  This is an automatic backport of pull request Fix flaky test TestFilestreamDelete #47828 done by Mergify.

[mergify]

Cherry-pick of 5ce630a has failed:

On branch mergify/bp/8.19/pr-47828
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Unmerged paths:
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	deleted by us:   filebeat/tests/integration/filestream_delete_test.go

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