Fix a missed case in int8-exp-three-digits.out, per buildfarm results.

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

@@ -726,13 +726,13 @@ SELECT CAST('42'::int2 AS int8), CAST('-37'::int2 AS int8);
 (1 row)
 
 SELECT CAST(q1 AS float4), CAST(q2 AS float8) FROM INT8_TBL;
-     q1      |          q2           
--------------+-----------------------
-         123 |                   456
-         123 |  4.56789012345679e+15
- 4.56789e+15 |                   123
- 4.56789e+15 |  4.56789012345679e+15
- 4.56789e+15 | -4.56789012345679e+15
+      q1      |           q2           
+--------------+------------------------
+          123 |                    456
+          123 |  4.56789012345679e+015
+ 4.56789e+015 |                    123
+ 4.56789e+015 |  4.56789012345679e+015
+ 4.56789e+015 | -4.56789012345679e+015
 (5 rows)
 
 SELECT CAST('36854775807.0'::float4 AS int8);