staking: fix comment in Uptime::missed_blocks (#4662)

Fix on #4279.

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## Checklist before requesting a review

- [X] If this code contains consensus-breaking changes, I have added the
"consensus-breaking" label. Otherwise, I declare my belief that there
are not consensus-breaking changes, for the following reason:

  > comment fix

crates/core/component/stake/src/uptime.rs

@@ -80,7 +80,7 @@ impl Uptime {
 
     /// Enumerates the missed blocks over the window in terms of absolute block height.
     pub fn missed_blocks(&self) -> impl Iterator<Item = u64> + DoubleEndedIterator + '_ {
-        // The height of the next block to be recorded (not yet recorded):
+        // The height of the latest block that's been recorded:
         let current_height = self.as_of_block_height;
         // The length of the window of blocks being recorded:
         let window_len = self.signatures.len();