[SPARK-57801] Upgrade fabric8 to 7.8.0

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

This PR aims to upgrade `fabric8` (Kubernetes Client) to 7.8.0.

### Why are the changes needed?

To bring the latest bug fixes and improvements.
- https://github.com/fabric8io/kubernetes-client/releases/tag/v7.8.0
  - fabric8io/kubernetes-client#7907
  - fabric8io/kubernetes-client#7847

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

No.

### How was this patch tested?

Pass the CIs.

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

Generated-by: Claude Opus 4.8

Closes #726 from dongjoon-hyun/SPARK-57801.

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

Author: dongjoon-hyun

gradle/libs.versions.toml

@@ -15,7 +15,7 @@
 # specific language governing permissions and limitations
 # under the License.
 [versions]
-fabric8 = "7.7.0"
+fabric8 = "7.8.0"
 lombok = "1.18.46"
 netty = "4.2.15.Final"
 operator-sdk = "5.3.5"