fix EmojiTransliterator return type compatibility with PHP 8.5

Author: xabbuh

Tests/Transliterator/EmojiTransliteratorTest.php

@@ -189,6 +189,6 @@ public function testGetErrorMessageWithUninitializedTransliterator()
     {
         $transliterator = EmojiTransliterator::create('emoji-en');
 
-        $this->assertFalse($transliterator->getErrorMessage());
+        $this->assertSame('', $transliterator->getErrorMessage());
     }
 }

Transliterator/EmojiTransliterator.php

@@ -70,14 +70,22 @@ public function createInverse(): self
             return self::create($this->id, self::REVERSE);
         }
 
+        /**
+         * @return int
+         */
+        #[\ReturnTypeWillChange]
         public function getErrorCode(): int|false
         {
             return isset($this->transliterator) ? $this->transliterator->getErrorCode() : 0;
         }
 
+        /**
+         * @return string
+         */
+        #[\ReturnTypeWillChange]
         public function getErrorMessage(): string|false
         {
-            return isset($this->transliterator) ? $this->transliterator->getErrorMessage() : false;
+            return isset($this->transliterator) ? $this->transliterator->getErrorMessage() : '';
         }
 
         public static function listIDs(): array