Fix lookup documentation in ERC20Votes and Checkpoints (#4218)

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>

contracts/token/ERC20/extensions/ERC20Votes.sol

@@ -114,7 +114,7 @@ abstract contract ERC20Votes is ERC20Permit, IERC5805 {
      * @dev Lookup a value in a list of (sorted) checkpoints.
      */
     function _checkpointsLookup(Checkpoint[] storage ckpts, uint256 timepoint) private view returns (uint256) {
-        // We run a binary search to look for the earliest checkpoint taken after `timepoint`.
+        // We run a binary search to look for the last (most recent) checkpoint taken before (or at) `timepoint`.
         //
         // Initially we check if the block is recent to narrow the search range.
         // During the loop, the index of the wanted checkpoint remains in the range [low-1, high).