Fix Rust E2E test for new ignore_whitespace field on WorkspacesDiffRequest

The 1.0.63 type regeneration added an optional ignore_whitespace field to
the generated WorkspacesDiffRequest struct. The explicit struct literal in
rpc_workspace_checkpoints.rs failed to compile (E0063: missing field), which
broke clippy on ubuntu and cargo test on macos/windows. Add ..Default::default()
to the literal, matching the existing pattern in rpc_session_state.rs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

rust/tests/e2e/rpc_workspace_checkpoints.rs

@@ -90,6 +90,7 @@ async fn should_return_typed_workspace_diff_result() {
                     .workspaces()
                     .diff(WorkspacesDiffRequest {
                         mode: WorkspaceDiffMode::Unstaged,
+                        ..Default::default()
                     })
                     .await
                     .expect("workspace diff");