test: fix flaky cases. (#16649)

close #16648

Fix the flaky test `raftstore::test_snap::test_v1_apply_snap_from_v2`.

Signed-off-by: lucasliang <nkcs_lykx@hotmail.com>

components/engine_rocks/src/checkpoint.rs

@@ -34,6 +34,8 @@ impl Checkpointer for RocksEngineCheckpointer {
         titan_out_dir: Option<&Path>,
         log_size_for_flush: u64,
     ) -> Result<()> {
+        #[cfg(any(test, feature = "testexport"))]
+        file_system::delete_dir_if_exist(db_out_dir).unwrap();
         self.0
             .create_at(db_out_dir, titan_out_dir, log_size_for_flush)
             .map_err(|e| r2e(e))