HBASE-28470 Fix typo in Java method comment (#5786)

Co-authored-by: voztaka <you@example.com>
Signed-off-by: Duo Zhang <zhangduo@apache.org>
(cherry picked from commit a34b4bc)

hbase-client/src/main/java/org/apache/hadoop/hbase/client/Admin.java

@@ -1163,7 +1163,7 @@ default void move(byte[] encodedRegionName, byte[] destServerName) throws IOExce
 
   /**
    * Unassign a Region.
-   * @param regionName Region name to assign.
+   * @param regionName Region name to unassign.
    * @throws IOException if a remote or network exception occurs
    */
   void unassign(byte[] regionName) throws IOException;