Fix a line that was missed when renaming. (#3174)

## Motivation

#3168 and #3169 were merged without rebasing on each other, breaking the
build.

## Proposal

Fix the broken line.

## Test Plan

With this and #3171 CI should work again.

## Release Plan

- Nothing to do / These changes follow the usual release cycle.

## Links

- [reviewer
checklist](https://github.com/linera-io/linera-protocol/blob/main/CONTRIBUTING.md#reviewer-checklist)

linera-core/src/unit_tests/worker_tests.rs

@@ -3553,7 +3553,7 @@ where
     let proposal = make_child_block(&change_ownership_value)
         .into_proposal_with_round(&KeyPair::generate(), Round::MultiLeader(0));
     let (executed_block, _) = worker
-        .stage_block_execution(proposal.content.proposal.clone())
+        .stage_block_execution(proposal.content.block.clone())
         .await?;
     let value = Hashed::new(ConfirmedBlock::new(executed_block));
     let (response, _) = worker.handle_block_proposal(proposal).await?;