fix(gc) - fix the chunk_tail <= tail invariant (#12207)

According to this line in the storage checker, the chunk tail should
always be less or equal than the tail:

https://github.com/near/nearcore/blob/99ecfa4e8b97eda5e369d82ef00cfc06e5291552/chain/chain/src/store_validator/validate.rs#L146

This invariant is broken, I'm guessing since #12025 as shown by nayduck
gc test failing at this check:
https://nayduck.nearone.org/#/test/108874 - test1 stderr last line

This is a simple mitigation but I'm not 100% sure if correct - please
let me know if it makes sense or not.

Even if not entirely correct it should not cause any problems. At worst
gc will attempt to clean a little bit more data that isn't there. I
hope.

The only real change here is the added `saturating_sub(1)` to the line
where we set the tail.

chain/chain/src/chain.rs

@@ -1679,7 +1679,13 @@ impl Chain {
 
         tracing::debug!(target: "sync", ?min_height_included, ?new_tail, "adjusting tail for missing chunks");
         new_tail = std::cmp::min(new_tail, min_height_included.saturating_sub(1));
-        let new_chunk_tail = prev_block.chunks().iter().map(|x| x.height_created()).min().unwrap();
+
+        // In order to find the right new_chunk_tail we need to find the minimum
+        // of chunk height_created for chunks in the new tail block.
+        let new_tail_block = self.get_block_by_height(new_tail)?;
+        let new_chunk_tail =
+            new_tail_block.chunks().iter().map(|chunk| chunk.height_created()).min().unwrap();
+
         let tip = Tip::from_header(prev_block.header());
         let final_head = Tip::from_header(self.genesis.header());
         // Update related heads now.