[fix](fe) Convert testCtePrivilegeCheck from JMockit to Mockito

### What problem does this PR solve?

Problem Summary: After PR #62221 removed all JMockit usage from the codebase,
the testCtePrivilegeCheck method still used JMockit Expectations pattern which
causes compilation failure. Convert to Mockito spy pattern consistent with
the rest of the test file.

### Release note

None

### Check List (For Author)

- Test: Unit Test (compilation verified)
- Behavior changed: No
- Does this need documentation: No

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: seawinde

fe/fe-core/src/test/java/org/apache/doris/nereids/privileges/TestCheckPrivileges.java

@@ -261,13 +261,10 @@ public void testCtePrivilegeCheck() throws Exception {
 
             AccessControllerManager accessManager = Env.getCurrentEnv().getAccessManager();
             CatalogAccessController catalogAccessController = accessManager.getAccessControllerOrDefault(catalog);
-            new Expectations(accessManager) {
-                {
-                    accessManager.getAccessControllerOrDefault("internal");
-                    minTimes = 0;
-                    result = catalogAccessController;
-                }
-            };
+            AccessControllerManager spyAccessManager = Mockito.spy(accessManager);
+            Mockito.doReturn(catalogAccessController).when(spyAccessManager)
+                    .getAccessControllerOrDefault("internal");
+            Deencapsulation.setField(Env.getCurrentEnv(), "accessManager", spyAccessManager);
 
             withPrivileges(privileges, () -> {
                 // CTE with authorized table should succeed