test(japan): exclude 2019 from emperorsBirthday random year range

In 2019, Emperor Akihito abdicated and no Emperor's Birthday holiday was
observed that year. The provider correctly returns nothing for 2019, but
testTranslation and testHolidayType used an unbounded
generateRandomYear(ESTABLISHMENT_YEAR) that could land on 2019, causing
intermittent failures.

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

Author: stelgenhof

tests/Japan/EmperorsBirthdayTest.php

@@ -139,10 +139,19 @@ public function testEmperorsBirthdayIn2019(): void
      */
     public function testTranslation(): void
     {
+        // Era 1: 1949–2018 (2019 is excluded — no Emperor's Birthday that year due to abdication)
         $this->assertTranslatedHolidayName(
             self::REGION,
             self::HOLIDAY,
-            static::generateRandomYear(self::ESTABLISHMENT_YEAR),
+            static::generateRandomYear(self::ESTABLISHMENT_YEAR, 2018),
+            [self::LOCALE => '天皇誕生日']
+        );
+
+        // Era 2: 2020+ (Emperor Naruhito's birthday, February 23)
+        $this->assertTranslatedHolidayName(
+            self::REGION,
+            self::HOLIDAY,
+            static::generateRandomYear(2020),
             [self::LOCALE => '天皇誕生日']
         );
     }
@@ -154,10 +163,19 @@ public function testTranslation(): void
      */
     public function testHolidayType(): void
     {
+        // Era 1: 1949–2018 (2019 is excluded — no Emperor's Birthday that year due to abdication)
+        $this->assertHolidayType(
+            self::REGION,
+            self::HOLIDAY,
+            static::generateRandomYear(self::ESTABLISHMENT_YEAR, 2018),
+            Holiday::TYPE_OFFICIAL
+        );
+
+        // Era 2: 2020+ (Emperor Naruhito's birthday, February 23)
         $this->assertHolidayType(
             self::REGION,
             self::HOLIDAY,
-            static::generateRandomYear(self::ESTABLISHMENT_YEAR),
+            static::generateRandomYear(2020),
             Holiday::TYPE_OFFICIAL
         );
     }