chore(chain)!: use debug_assert! on apply_update

As mentioned in issue #1689 the `debug_assert!` is being used on other
`LocalChain` methods, such as: `from_changeset`, and `apply_changeset`
but it was missing on `apply_update`.

Author: oleonardolima

crates/chain/src/local_chain.rs

@@ -174,7 +174,7 @@ impl LocalChain {
     pub fn apply_update(&mut self, update: CheckPoint) -> Result<ChangeSet, CannotConnectError> {
         let (new_tip, changeset) = merge_chains(self.tip.clone(), update)?;
         self.tip = new_tip;
-        self._check_changeset_is_applied(&changeset);
+        debug_assert!(self._check_changeset_is_applied(&changeset));
         Ok(changeset)
     }