Fix mocks in ProjectVersionRefUpdateTest

Fix an incorrect mocking in ProjectVersionRefUpdateTest that
produced a fatal error about unnecessary stubbings.

Change-Id: I1c03cb18aca638ed32935d600f180d0340743ea2

src/test/java/com/googlesource/gerrit/plugins/multisite/validation/ProjectVersionRefUpdateTest.java

diff --git a/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/ProjectVersionRefUpdateTest.java b/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/ProjectVersionRefUpdateTest.java
index da8c8a9..90e3274 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/ProjectVersionRefUpdateTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/ProjectVersionRefUpdateTest.java
@@ -129,7 +129,7 @@
             A_TEST_PROJECT_NAME_KEY, ProjectVersionRefUpdate.MULTI_SITE_VERSIONING_VALUE_REF))
         .thenReturn(false);
 
-    when(sharedRefDb.compareAndPut(any(Project.NameKey.class), isNull(), any(ObjectId.class)))
+    when(sharedRefDb.compareAndPut(any(Project.NameKey.class), any(Ref.class), any(ObjectId.class)))
         .thenReturn(true);
     when(sharedRefDb.compareAndPut(any(Project.NameKey.class), any(String.class), any(), any()))
         .thenReturn(true);