Update int8-exp-three-digits.out to match new contents of int8.out.

src/test/regress/expected/int8-exp-three-digits.out

@@ -802,3 +802,16 @@ SELECT * FROM generate_series('+4567890123456789'::int8, '+4567890123456799'::in
  4567890123456799
 (6 rows)
 
+-- corner case
+SELECT (-1::int8<<63)::text;
+         text         
+----------------------
+ -9223372036854775808
+(1 row)
+
+SELECT ((-1::int8<<63)+1)::text;
+         text         
+----------------------
+ -9223372036854775807
+(1 row)
+