[ VM / Service ] Fixed mismatching type in migrated NNBD service code
[ VM / Service ] Fixed mismatching type in migrated NNBD service code

Change-Id: If2bd92c48893adf46a7fe08e725d908f50317e2d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/134782
Reviewed-by: Ryan Macnak <d738b7f001baf9789095d7dc549cff6de60b011d@google.com>
Reviewed-by: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk