debug.rs: make one of the imports optional

This removes a warning rust-analyzer otherwise shows me.

cli/src/commands/debug.rs

@@ -19,7 +19,7 @@ use std::io::Write as _;
 use clap::Subcommand;
 use jj_lib::backend::ObjectId;
 use jj_lib::default_index_store::{DefaultIndexStore, ReadonlyIndexWrapper};
-use jj_lib::local_working_copy::{LocalWorkingCopy, LockedLocalWorkingCopy};
+use jj_lib::local_working_copy::LocalWorkingCopy;
 use jj_lib::revset;
 use jj_lib::working_copy::WorkingCopy;
 
@@ -276,6 +276,8 @@ fn cmd_debug_watchman(
     command: &CommandHelper,
     subcommand: &DebugWatchmanSubcommand,
 ) -> Result<(), CommandError> {
+    use jj_lib::local_working_copy::LockedLocalWorkingCopy;
+
     let mut workspace_command = command.workspace_helper(ui)?;
     let repo = workspace_command.repo().clone();
     match subcommand {