[Cherry-pick][2.23] feat: improve llamastack fms guardrails provider tests

[rhods-ci-bot]

Cherry-picked #474 into 2.23. Requested by: adolfo-ab

[github-actions]

The following are automatically added/executed:

• PR size label.
• Run pre-commit
• Run tox
• Add PR author as the PR assignee
• Build image based on the PR

Available user actions:

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  lgtm label removed on each new commit push.
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Supported labels

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[github-actions]

Status of building tag 2.23: success.
Status of pushing tag 2.23 to image registry: success.