Flaky Test: BackendServiceMetricSuite - backend service metric test

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

### Search before asking

- [X] I have searched in the [issues](https://github.com/apache/incubator-kyuubi/issues?q=is%3Aissue) and found no similar issues.

### Describe the bug

```
BackendServiceMetricSuite:
- backend service metric test *** FAILED ***
java.io.FileNotFoundException: /home/runner/work/incubator-kyuubi/incubator-kyuubi/kyuubi-server/target/tmp/kyuubi-538c9d61-cd4d-449d-b3d4-33f49b4377ca/report.json (No such file or directory)
```

### Affects Version(s)

1.6.0

### Kyuubi Server Log Output

_No response_

### Kyuubi Engine Log Output

_No response_

### Kyuubi Server Configurations

_No response_

### Kyuubi Engine Configurations

_No response_

### Additional context

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

Start by locating and running BackendServiceMetricSuite, then inspect why the temporary report.json path under kyuubi-server/target/tmp is absent when the backend service metric test runs. Done means the test reliably produces and reads the expected report without intermittent FileNotFoundException failures.

Written by the indexing model from the issue text.