Fix another typo in e0b1ee1

Reported-by: Richard Guo
Discussion: https://postgr.es/m/CAMbWs4_kHMJDak75y1kBTirv-drS1-knT-7Mpg5LprAjqRJDVA%40mail.gmail.com

Author: akorotkov

src/backend/access/nbtree/nbtsearch.c

@@ -1784,7 +1784,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 			/*
 			 * If the result of prechecking required keys was true, then in
 			 * assert-enabled builds we also recheck that _bt_checkkeys()
-			 * result is is the same.
+			 * result is the same.
 			 */
 			Assert(!requiredMatchedByPrecheck ||
 				   passes_quals == _bt_checkkeys(scan, itup, indnatts, dir,