add to lastModified checked exception list

BUG=331420990
PiperOrigin-RevId: 623179939
Change-Id: I1500d8d2ceebeae63d8d9bf56f5376ce18e823d9

Author: jeyoungk

java/com/google/copybara/DestinationReader.java

@@ -157,10 +157,8 @@ public abstract void copyDestinationFilesToDirectory(Glob glob, Path directory)
   @SuppressWarnings("unused")
   public abstract boolean exists(String path);
 
-  /**
-   * Fetch the destination version at which this file was last modified.
-   */
-  public String lastModified(String path) throws IOException {
+  /** Fetch the destination version at which this file was last modified. */
+  public String lastModified(String path) throws IOException, RepoException {
     throw new UnsupportedOperationException(
         "Last modified is not implemented in this destination reader.");
   }