fix func_time.test to be independent from the system time zone

mysql-test/r/func_time.result

@@ -2004,6 +2004,7 @@ a
 2000-02-23
 2005-05-04
 DROP TABLE t1;
+SET TIME_ZONE='+02:00';
 #
 # MDEV-6302 Wrong result set when using GROUP BY FROM_UNIXTIME(...)+0
 #
@@ -2011,8 +2012,8 @@ CREATE TABLE t1 (a DATE);
 INSERT INTO t1 VALUES ('2005-05-04'),('2000-02-23');
 SELECT a, FROM_UNIXTIME(CONCAT(a,'10')) AS f1, FROM_UNIXTIME(CONCAT(a,'10'))+0 AS f2 FROM t1;
 a	f1	f2
-2005-05-04	1970-01-01 03:33:25	19700101033325.000000
-2000-02-23	1970-01-01 03:33:20	19700101033320.000000
+2005-05-04	1970-01-01 02:33:25	19700101023325.000000
+2000-02-23	1970-01-01 02:33:20	19700101023320.000000
 SELECT * FROM t1 GROUP BY FROM_UNIXTIME(CONCAT(a,'10'))+0;
 a
 2000-02-23
@@ -2046,7 +2047,6 @@ DROP TABLE t1,t2;
 #
 # MDEV-4635 Crash in UNIX_TIMESTAMP(STR_TO_DATE('2020','%Y'))
 #
-SET TIME_ZONE='+02:00';
 SELECT UNIX_TIMESTAMP(STR_TO_DATE('2020','%Y'));
 UNIX_TIMESTAMP(STR_TO_DATE('2020','%Y'))
 NULL

mysql-test/t/func_time.test

@@ -1212,6 +1212,7 @@ SELECT * FROM t1 GROUP BY @a:=(FROM_UNIXTIME(concat(a,'10'))*1);
 
 DROP TABLE t1;
 
+SET TIME_ZONE='+02:00';
 
 --echo #
 --echo # MDEV-6302 Wrong result set when using GROUP BY FROM_UNIXTIME(...)+0
@@ -1239,10 +1240,9 @@ DROP TABLE t1,t2;
 --echo #
 --echo # MDEV-4635 Crash in UNIX_TIMESTAMP(STR_TO_DATE('2020','%Y'))
 --echo #
-SET TIME_ZONE='+02:00';
 SELECT UNIX_TIMESTAMP(STR_TO_DATE('2020','%Y'));
-SET TIME_ZONE=DEFAULT;
 
+SET TIME_ZONE=DEFAULT;
 
 --echo #
 --echo #  MDEV-4863 COALESCE(time_or_datetime) returns wrong results in numeric context