CVE-2026-48892: Apache Airflow: Config API leaks per-key secrets backend kwargs - masker bypass on synthetic options

The Config API in Apache Airflow surfaced per-key secrets-backend overrides (environment variables like `AIRFLOW__SECRETS__BACKEND_KWARG__SECRET_ID` and `AIRFLOW__WORKERS__SECRETS_BACKEND_KWARG__SECRET_ID`) as synthetic config options whose option names were not in `sensitive_config_values`, so the masker did not redact them. An authenticated UI/API user with Config read permission could retrieve plaintext secrets-backend credentials (Vault `role_id` / `secret_id`, etc.) from the Config API output. Affects deployments that configure secrets backends via per-key environment overrides. Users are advised to upgrade to `apache-airflow` 3.3.0 or later.