Stabilize timetz test across DST transitions.

The timetz test cases I added in commit a9632830 were unintentionally
sensitive to whether or not DST is active in the PST8PDT time zone.
Thus, they'll start failing this coming weekend, as reported by
Bernhard M. Wiedemann in bug #16689.  Fortunately, DST-awareness is
not significant to the purpose of these test cases, so we can just
force them all to PDT (DST hours) to preserve stability of the
results.

Back-patch to v10, as the prior patch was.

Discussion: https://postgr.es/m/16689-57701daa23b377bf@postgresql.org

src/test/regress/expected/timetz.out

@@ -91,45 +91,45 @@ SELECT f1 AS "Ten" FROM TIMETZ_TBL WHERE f1 >= '00:00-07';
 (12 rows)
 
 -- Check edge cases
-SELECT '23:59:59.999999'::timetz;
+SELECT '23:59:59.999999 PDT'::timetz;
        timetz       
 --------------------
  23:59:59.999999-07
 (1 row)
 
-SELECT '23:59:59.9999999'::timetz;  -- rounds up
+SELECT '23:59:59.9999999 PDT'::timetz;  -- rounds up
    timetz    
 -------------
  24:00:00-07
 (1 row)
 
-SELECT '23:59:60'::timetz;  -- rounds up
+SELECT '23:59:60 PDT'::timetz;  -- rounds up
    timetz    
 -------------
  24:00:00-07
 (1 row)
 
-SELECT '24:00:00'::timetz;  -- allowed
+SELECT '24:00:00 PDT'::timetz;  -- allowed
    timetz    
 -------------
  24:00:00-07
 (1 row)
 
-SELECT '24:00:00.01'::timetz;  -- not allowed
-ERROR:  date/time field value out of range: "24:00:00.01"
-LINE 1: SELECT '24:00:00.01'::timetz;
+SELECT '24:00:00.01 PDT'::timetz;  -- not allowed
+ERROR:  date/time field value out of range: "24:00:00.01 PDT"
+LINE 1: SELECT '24:00:00.01 PDT'::timetz;
                ^
-SELECT '23:59:60.01'::timetz;  -- not allowed
-ERROR:  date/time field value out of range: "23:59:60.01"
-LINE 1: SELECT '23:59:60.01'::timetz;
+SELECT '23:59:60.01 PDT'::timetz;  -- not allowed
+ERROR:  date/time field value out of range: "23:59:60.01 PDT"
+LINE 1: SELECT '23:59:60.01 PDT'::timetz;
                ^
-SELECT '24:01:00'::timetz;  -- not allowed
-ERROR:  date/time field value out of range: "24:01:00"
-LINE 1: SELECT '24:01:00'::timetz;
+SELECT '24:01:00 PDT'::timetz;  -- not allowed
+ERROR:  date/time field value out of range: "24:01:00 PDT"
+LINE 1: SELECT '24:01:00 PDT'::timetz;
                ^
-SELECT '25:00:00'::timetz;  -- not allowed
-ERROR:  date/time field value out of range: "25:00:00"
-LINE 1: SELECT '25:00:00'::timetz;
+SELECT '25:00:00 PDT'::timetz;  -- not allowed
+ERROR:  date/time field value out of range: "25:00:00 PDT"
+LINE 1: SELECT '25:00:00 PDT'::timetz;
                ^
 --
 -- TIME simple math

src/test/regress/sql/timetz.sql

@@ -36,14 +36,14 @@ SELECT f1 AS "None" FROM TIMETZ_TBL WHERE f1 < '00:00-07';
 SELECT f1 AS "Ten" FROM TIMETZ_TBL WHERE f1 >= '00:00-07';
 
 -- Check edge cases
-SELECT '23:59:59.999999'::timetz;
-SELECT '23:59:59.9999999'::timetz;  -- rounds up
-SELECT '23:59:60'::timetz;  -- rounds up
-SELECT '24:00:00'::timetz;  -- allowed
-SELECT '24:00:00.01'::timetz;  -- not allowed
-SELECT '23:59:60.01'::timetz;  -- not allowed
-SELECT '24:01:00'::timetz;  -- not allowed
-SELECT '25:00:00'::timetz;  -- not allowed
+SELECT '23:59:59.999999 PDT'::timetz;
+SELECT '23:59:59.9999999 PDT'::timetz;  -- rounds up
+SELECT '23:59:60 PDT'::timetz;  -- rounds up
+SELECT '24:00:00 PDT'::timetz;  -- allowed
+SELECT '24:00:00.01 PDT'::timetz;  -- not allowed
+SELECT '23:59:60.01 PDT'::timetz;  -- not allowed
+SELECT '24:01:00 PDT'::timetz;  -- not allowed
+SELECT '25:00:00 PDT'::timetz;  -- not allowed
 
 --
 -- TIME simple math