Add tests for date_part of epoch near upper bound of timestamp range

This exercises a special case in the implementations of
date_part('epoch', timestamp[tz]) that was previously not tested.

src/test/regress/expected/timestamp.out

@@ -1012,6 +1012,13 @@ SELECT d1 as "timestamp",
  Mon Jan 01 17:32:01 2001    |       200 |        21 |          3 |   2451912 |    978370321
 (65 rows)
 
+-- value near upper bound uses special case in code
+SELECT date_part('epoch', '294270-01-01 00:00:00'::timestamp);
+   date_part   
+---------------
+ 9224097091200
+(1 row)
+
 -- TO_CHAR()
 SELECT to_char(d1, 'DAY Day day DY Dy dy MONTH Month month RM MON Mon mon')
    FROM TIMESTAMP_TBL;

src/test/regress/expected/timestamptz.out

@@ -1189,6 +1189,13 @@ SELECT d1 as timestamptz,
  Mon Jan 01 17:32:01 2001 PST    |   -28800 |            -8 |               0
 (66 rows)
 
+-- value near upper bound uses special case in code
+SELECT date_part('epoch', '294270-01-01 00:00:00+00'::timestamptz);
+   date_part   
+---------------
+ 9224097091200
+(1 row)
+
 -- TO_CHAR()
 SELECT to_char(d1, 'DAY Day day DY Dy dy MONTH Month month RM MON Mon mon')
    FROM TIMESTAMPTZ_TBL;

src/test/regress/sql/timestamp.sql

@@ -261,6 +261,9 @@ SELECT d1 as "timestamp",
    date_part( 'epoch', d1) AS epoch
    FROM TIMESTAMP_TBL;
 
+-- value near upper bound uses special case in code
+SELECT date_part('epoch', '294270-01-01 00:00:00'::timestamp);
+
 -- TO_CHAR()
 SELECT to_char(d1, 'DAY Day day DY Dy dy MONTH Month month RM MON Mon mon')
    FROM TIMESTAMP_TBL;

src/test/regress/sql/timestamptz.sql

@@ -275,6 +275,9 @@ SELECT d1 as timestamptz,
    date_part( 'timezone_minute', d1) AS timezone_minute
    FROM TIMESTAMPTZ_TBL;
 
+-- value near upper bound uses special case in code
+SELECT date_part('epoch', '294270-01-01 00:00:00+00'::timestamptz);
+
 -- TO_CHAR()
 SELECT to_char(d1, 'DAY Day day DY Dy dy MONTH Month month RM MON Mon mon')
    FROM TIMESTAMPTZ_TBL;