chunk_trace: add wait in test to avoid use after free in lib callback.

[pwhelan]

Summary

This one liner should fix the sporadic CI failures in the `flb-rt-core_chunk_trace' test. The crash occurs when the flb_lib based input uses the records structure after the test has exited and freed them. I added a sleep to avoid this scenario.

At the very least it ran around 725 times in succession without any further errors:

while ./bin/flb-rt-core_chunk_trace > error.log 2>&1 ; do echo -n "." ; done
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.............................................^C

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Testing
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Backporting

• Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.