Fix ls-user-ref and use the correct identity for listing refs

The ls-user-ref was broken by Change-Id: I1819de0bab where
the refactoring of the permission backend needed to be passed
the current user as parameter. As a result, the LsUserRefs, started
using the user's identity executing the command instead of the one
requested as a parameter.

Bug: Issue 11235
Change-Id: I48b6e14a2fe24d3d2a96a8274bd9e0108dc0c95d

java/com/google/gerrit/sshd/commands/LsUserRefs.java

@@ -92,7 +92,7 @@ public class LsUserRefs extends SshCommand {
       try {
         Map<String, Ref> refsMap =
             permissionBackend
-                .user(user)
+                .user(ctx.getUser())
                 .project(projectName)
                 .filter(repo.getRefDatabase().getRefs(ALL), repo, RefFilterOptions.defaults());