fix(south korea): fix twoDaysLaterNewYearsDay test

`twoDaysLaterNewYearsDay` was celebrated until 1989, not in 1990 anymore,
while the test was set to and including 1990. When the year 1990 is picked,
`twoDaysLaterNewYearsDay` won't exists, causing the test to fail.

Signed-off-by: Sacha Telgenhof <me@sachatelgenhof.com>

Author: stelgenhof

tests/SouthKorea/NewYearsDayTest.php

@@ -59,7 +59,7 @@ public function testHoliday(): void
         }
 
         // Two days later New Year's Day
-        if ($year <= 1990) {
+        if ($year <= 1989) {
             $this->assertHoliday(
                 self::REGION,
                 'twoDaysLaterNewYearsDay',
@@ -84,7 +84,7 @@ public function testHolidayAfterRemoval(): void
         $this->assertNotHoliday(
             self::REGION,
             'twoDaysLaterNewYearsDay',
-            $this->generateRandomYear(1991)
+            $this->generateRandomYear(1990)
         );
     }