ORC-2084: Upgrade mockito to 5.21.0

### What changes were proposed in this pull request?

This PR aims to upgrade `mockito` to 5.21.0.

### Why are the changes needed?

To use the latest bug fixed version.

### How was this patch tested?

Pass the CIs.

### Was this patch authored or co-authored using generative AI tooling?

`Gemini 3 Pro (High)` on `Antigravity`

Closes #2523 from dongjoon-hyun/ORC-2084.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: dongjoon-hyun

java/pom.xml

@@ -83,7 +83,7 @@
     <maven.compiler.useIncrementalCompilation>false</maven.compiler.useIncrementalCompilation>
     <maven.version>3.9.12</maven.version>
 
-    <mockito.version>5.10.0</mockito.version>
+    <mockito.version>5.21.0</mockito.version>
     <orc-format.version>1.1.1</orc-format.version>
     <!-- Build Properties -->
     <project.build.outputTimestamp>2025-07-08T15:22:41Z</project.build.outputTimestamp>