fix(electrum): fixed chain sync issue

Fixed a logic error in `construct_update_tip` in `electrum_ext.rs` that caused
the local chain tip to always be a block behind the newest confirmed block.

crates/electrum/src/electrum_ext.rs

@@ -305,7 +305,7 @@ fn construct_update_tip(
     // Atomically fetch the latest `ASSUME_FINAL_DEPTH` count of blocks from Electrum. We use this
     // to construct our checkpoint update.
     let mut new_blocks = {
-        let start_height = new_tip_height.saturating_sub(ASSUME_FINAL_DEPTH);
+        let start_height = (new_tip_height + 1).saturating_sub(ASSUME_FINAL_DEPTH);
         let hashes = client
             .block_headers(start_height as _, ASSUME_FINAL_DEPTH as _)?
             .headers