[SPARK-56096] Upgrade mockito to 5.23.0

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

This PR upgrades `mockito` to 5.23.0 to bring Java 25 related bug fix.

### Why are the changes needed?

To keep the test dependency up to date with the latest bug fixes.
- https://github.com/mockito/mockito/releases/tag/v5.23.0
- https://github.com/mockito/mockito/releases/tag/v5.22.0
  - mockito/mockito#3778
  - mockito/mockito#3785

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Pass the CIs with the existing tests.

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

Generated-by: Claude Code (claude-opus-4-6)

Closes #557 from dongjoon-hyun/SPARK-56096.

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

Author: dongjoon-hyun

gradle/libs.versions.toml

@@ -28,7 +28,7 @@ slf4j = "2.0.17"
 # Test
 junit = "6.0.0"
 jacoco = "0.8.14"
-mockito = "5.21.0"
+mockito = "5.23.0"
 
 # Build Analysis
 checkstyle = "13.2.0"