Fix potential overflow in update_next_xid (#6412)

## Problem

See https://neondb.slack.com/archives/C06F5UJH601/p1705731304237889

Adding 1 to xid in `update_next_xid` can cause overflow in debug mode.
0xffffffff is valid transaction ID.

## Summary of changes

Use `wrapping_add` 

## Checklist before requesting a review

- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.

## Checklist before merging

- [ ] Do not forget to reformat commit message to not include the above
checklist

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>

libs/postgres_ffi/src/xlog_utils.rs

@@ -329,8 +329,8 @@ impl CheckPoint {
     ///
     /// Returns 'true' if the XID was updated.
     pub fn update_next_xid(&mut self, xid: u32) -> bool {
-        // nextXid should nw greater than any XID in WAL, so increment provided XID and check for wraparround.
-        let mut new_xid = std::cmp::max(xid + 1, pg_constants::FIRST_NORMAL_TRANSACTION_ID);
+        // nextXid should be greater than any XID in WAL, so increment provided XID and check for wraparround.
+        let mut new_xid = std::cmp::max(xid.wrapping_add(1), pg_constants::FIRST_NORMAL_TRANSACTION_ID);
         // To reduce number of metadata checkpoints, we forward align XID on XID_CHECKPOINT_INTERVAL.
         // XID_CHECKPOINT_INTERVAL should not be larger than BLCKSZ*CLOG_XACTS_PER_BYTE
         new_xid =