Simplify-code findings:
- _authenticated_json: replace manual header construction with
self._headers(include_tenant=False) — eliminates duplication with
_headers() and includes Content-Type consistently.
- _health_requires_credentials: replace getattr(exc, 'status_code')
with _status_code_from_error(exc) for consistency with the existing
error-classification utility. Drop the fragile string-matching
fallback — _parse_response always sets status_code on
_OpenVikingHTTPError, so 401/403 check is sufficient.
- Relax test header assertions to check presence/absence of specific
headers rather than exact dict equality, so they survive the
header-construction refactor.
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