Two pre-existing tests codified the pre-fix behavior where any caller-
supplied metadata.tags would flow through to spend logs and routing:
- test_add_key_or_team_level_spend_logs_metadata_to_request exercised
the request/key/team tag merge. Set allow_client_tags=True on the key
metadata so the merge path is still tested under the new regime.
- test_create_file_with_nested_litellm_metadata asserted that
litellm_metadata[tags] form-data propagated to the handler. Drop the
tag field; the test still proves nested form-parser correctness via
spend_logs_metadata and environment.