chore: clean up getattr usage / drop test_llama_guard_output_action_metadata_is_registration_only in tests/test_llama_guard.py

Summary

In tests/test_llama_guard.py, the test test_llama_guard_output_action_metadata_is_registration_only uses getattr(llama_guard_check_output, "action_meta") to inspect the registration metadata of the llama_guard_check_output action.

This pattern was flagged by static analysis (Ruff B009 — "Do not call getattr with a constant attribute value") since @action() always assigns the action_meta attribute, so direct attribute access (llama_guard_check_output.action_meta) would be safe and idiomatic.

During review of PR #2151, it was agreed that this is pre-existing behavior and out of scope for that PR, and that the test itself should eventually be dropped rather than just fixed for style.

Rationale

• Removes reliance on getattr with a constant attribute name, resolving the Ruff B009 lint warning.
• test_llama_guard_output_action_metadata_is_registration_only may no longer be needed once the underlying registration-metadata contract is validated elsewhere (e.g., via shared action-registration tests), so removing/replacing it should be considered rather than just patching the lint issue.

Affected areas

• tests/test_llama_guard.py

Acceptance criteria

• Either:
  • Replace getattr(llama_guard_check_output, "action_meta") with direct attribute access llama_guard_check_output.action_meta, or
  • Remove test_llama_guard_output_action_metadata_is_registration_only if it is deemed redundant with other action-registration-metadata coverage.
• No new Ruff/lint warnings introduced.
• Existing test suite continues to pass.

References

• PR: https://github.com/NVIDIA-NeMo/Guardrails/pull/2151
• Review comment: https://github.com/NVIDIA-NeMo/Guardrails/pull/2151#discussion_r3585336541
• Requested by: @Pouyanpi