update CHANGELOG with PR number #5091

Assisted-by: Claude Sonnet 4.6

Author: MikeGoldsmith

CHANGELOG.md

@@ -13,7 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Unreleased
 
 - `opentelemetry-sdk`: fix YAML structure injection via environment variable substitution in declarative file configuration; values containing newlines are now emitted as quoted YAML scalars per spec requirement
-  ([#TODO](https://github.com/open-telemetry/opentelemetry-python/pull/TODO))
+  ([#5091](https://github.com/open-telemetry/opentelemetry-python/pull/5091))
 - `opentelemetry-sdk`: Add `create_logger_provider`/`configure_logger_provider` to declarative file configuration, enabling LoggerProvider instantiation from config files without reading env vars
   ([#4990](https://github.com/open-telemetry/opentelemetry-python/pull/4990))
 - `opentelemetry-sdk`: Add `service` resource detector support to declarative file configuration via `detection_development.detectors[].service`