chore: add missing symbols in pallets/parachain-staking/src/lib.rs (#727)

## fixes KILTProtocol/ticket#312



Add missing symbols in pallets/parachain-staking/src/lib.rs


## Metadata Diff to Develop Branch

<details>
<summary>Peregrine Diff</summary>

```

```

</details>

<details>
<summary>Spiritnet Diff</summary>

```
```

</details>

## Checklist:

- [ ] I have verified that the code works
- [ ] No panics! (checked arithmetic ops, no indexing `array[3]` use
`get(3)`, ...)
- [ ] I have verified that the code is easy to understand
  - [ ] If not, I have left a well-balanced amount of inline comments
- [ ] I have [left the code in a better
state](https://deviq.com/principles/boy-scout-rule)
- [ ] I have documented the changes (where applicable)
* Either PR or Ticket to update [the
Docs](https://github.com/KILTprotocol/docs)
    * Link the PR/Ticket here

Co-authored-by: Adel Golghalyani <48685760+Ad96el@users.noreply.github.com>

Author: hongmengning

pallets/parachain-staking/src/lib.rs

@@ -297,7 +297,7 @@ pub mod pallet {
 		/// NOTE: To protect against irremovability of a candidate or delegator,
 		/// we only allow for MaxUnstakeRequests - 1 many manual unstake
 		/// requests. The last one serves as a placeholder for the cases of
-		/// calling either `kick_delegator`, force_remove_candidate` or
+		/// calling either `kick_delegator`, `force_remove_candidate` or
 		/// `execute_leave_candidates`. Otherwise, a user could max out their
 		/// unstake requests and prevent themselves from being kicked from the
 		/// set of candidates/delegators until they unlock their funds.