Fix comment on B-tree insertion fastpath condition.

The comment earlier in the function correctly states "and the insertion
key is strictly greater than the first key in this page". That is what
we check here, not "greater than or equal".

src/backend/access/nbtree/nbtinsert.c

@@ -171,9 +171,9 @@ top:
 
 			/*
 			 * Check if the page is still the rightmost leaf page, has enough
-			 * free space to accommodate the new tuple, no split is in progress
-			 * and the scankey is greater than or equal to the first key on the
-			 * page.
+			 * free space to accommodate the new tuple, no split is in
+			 * progress, and the insertion scan key is strictly greater than
+			 * the first key on the page.
 			 */
 			if (P_ISLEAF(lpageop) && P_RIGHTMOST(lpageop) &&
 				!P_INCOMPLETE_SPLIT(lpageop) &&