Update CHANGELOG.md for #18818

CHANGELOG.md

@@ -10,6 +10,7 @@ FEATURES:
 ENHANCEMENTS:
 
 * aws/resource_aws_appconfig_deployment: Add `state` attribute ([#20288](https://github.com/hashicorp/terraform-provider-aws/issues/20288))
+* resource/aws_db_parameter_group: Allow parameter values to be mixed case, prioritize certain parameters when chunking, and avoid diffs with mixed-case parameter names ([#18818](https://github.com/hashicorp/terraform-provider-aws/issues/18818))
 * resource/aws_dms_endpoint: Add `s3_settings.data_format`, `s3_settings.parquet_timestamp_in_millisecond`, `s3_settings.parquet_version`, `s3_settings.encryption_mode` and `s3_settings.server_side_encryption_kms_key_id` arguments. ([#17591](https://github.com/hashicorp/terraform-provider-aws/issues/17591))
 * resource/aws_lambda_function: Add support for `python3.9` `runtime` value ([#20593](https://github.com/hashicorp/terraform-provider-aws/issues/20593))
 * resource/aws_lambda_layer_version: Add support for `python3.9` `compatible_runtimes` value ([#20593](https://github.com/hashicorp/terraform-provider-aws/issues/20593))