DAOS-623 test: add allowed error for FI (#17959)

[mchaarawi]

Steps for the author:

• Commit message follows the guidelines.
• Appropriate Features or Test-tag pragmas were used.
• Appropriate Functional Test Stages were run.
• At least two positive code reviews including at least one code owner from each category referenced in the PR.
• Testing is complete. If necessary, forced-landing label added and a reason added in a comment.

After all prior steps are complete:

• Gatekeeper requested (daos-gatekeeper added as a reviewer).

[github-actions]

Ticket title is 'Generic ticket for minor code cleanup and improvement'
Status is 'Resolved'
Labels: 'request_for_2.6.5,request_for_2.6.6,request_for_2.8,scrubbed_2.6.5'
Job should run at elevated priority (1)
https://daosio.atlassian.net/browse/DAOS-623