Use Java 21 Javadoc location for reference (#7)

Author: marchof

src/test/java/io/javaalmanac/javadoclink/JavaDocLinkTest.java

@@ -124,7 +124,7 @@ private boolean hasNoElement(Document doc, String element, String attr, String v
 		JDK_API_DOC.put("18", "https://docs.oracle.com/en/java/javase/18/docs/api/");
 		JDK_API_DOC.put("19", "https://docs.oracle.com/en/java/javase/19/docs/api/");
 		JDK_API_DOC.put("20", "https://docs.oracle.com/en/java/javase/20/docs/api/");
-		JDK_API_DOC.put("21", "https://download.java.net/java/early_access/jdk21/docs/api/");
+		JDK_API_DOC.put("21", "https://docs.oracle.com/en/java/javase/21/docs/api/");
 		JDK_API_DOC.put("22", "https://download.java.net/java/early_access/jdk22/docs/api/");
 	}