cleanup: fix an unused import on Windows
`OperationId` is only used in `test_snapshot_special_file()`, which
doesn't run (or even  build) on Windows.
@@ -23,7 +23,9 @@ use std::sync::Arc;
use itertools::Itertools;
use jujutsu_lib::backend::{Conflict, ConflictPart, TreeValue};
use jujutsu_lib::gitignore::GitIgnoreFile;
-use jujutsu_lib::op_store::{OperationId, WorkspaceId};
+#[cfg(unix)]
+use jujutsu_lib::op_store::OperationId;
+use jujutsu_lib::op_store::WorkspaceId;
use jujutsu_lib::repo::ReadonlyRepo;
use jujutsu_lib::repo_path::{RepoPath, RepoPathComponent, RepoPathJoin};
use jujutsu_lib::settings::UserSettings;
