YQL-20743: Fix negative UTC offset for %z specifier

commit_hash:ec3e4a5d1fabee8a46027aab303cfa49326a5a81

Author: igormunkin

yql/essentials/udfs/common/datetime2/datetime_udf.cpp

@@ -2918,7 +2918,7 @@ class TFormat: public TBoxedValue {
                                 return Size;
                             }
 
-                            *out++ = shift > 0 ? '+' : '-';
+                            *out++ = shift >= 0 ? '+' : '-';
                             shift = std::abs(shift);
                             out += PrintNDigits<2U>::Do(shift / 60U, out);
                             out += PrintNDigits<2U>::Do(shift % 60U, out);

yql/essentials/udfs/common/datetime2/test/canondata/test.test_Format_/results.txt

@@ -26,6 +26,11 @@
                             "% year 1970 monthFullName January monthShortName Jan month 01 day 01 hours 00 minutes 00 seconds 00 tz +0000 tzname GMT text"
                         ]
                     ];
+                    [
+                        [
+                            "% year 1970 monthFullName January monthShortName Jan month 01 day 01 hours 00 minutes 00 seconds 00 tz +0000 tzname UTC text"
+                        ]
+                    ];
                     [
                         [
                             "% year 2018 monthFullName December monthShortName Dec month 12 day 01 hours 01 minutes 02 seconds 03.456789 tz +0300 tzname Europe/Moscow text"

yql/essentials/udfs/common/datetime2/test/cases/Format.in

@@ -1,4 +1,5 @@
 {"ftztimestamp" = "1970-01-01T00:00:00,GMT"};
+{"ftztimestamp" = "1970-01-01T00:00:00,UTC"};
 {"ftztimestamp" = "2018-12-01T01:02:03.456789,Europe/Moscow"};
 {"ftztimestamp" = "2011-03-13T02:15:00,America/Los_Angeles"};
 {"ftztimestamp" = "2011-11-06T01:15:00,America/Los_Angeles"};