[Bug]: InputSandbox files are not uploaded when submitting a job

### Search before creating an issue

- [x] I have searched existing issues and confirmed this is not a duplicate

### Bug Description

When submitting a job with a file in `InputSandbox`, the file is never uploaded to the SandboxStore.
The JobWrapper reports `Total size of input sandbox: 0.00 MiB (0 bytes)` and the job fails because the executable file is not found on the worker node.

### Steps to Reproduce

1. Submit a job with an `InputSandbox` using the diracx CLI
2. The job will fail and you need to look at the Pilot StdOut

### Expected Behavior

The `InputSandBox` is uploaded and used for the job execution.

### Actual Behavior

The job fail with this :
```bash
2026-05-27T08:46:17,296669Z None/[69]JobWrapper INFO: Starting Job Wrapper Initialization for Job 69
2026-05-27T08:46:17,518793Z None/[69]JobWrapper INFO: Downloading InputSandbox for job 69: script.sh
2026-05-27T08:46:17,519979Z None/[69]JobWrapper INFO: Total size of input sandbox: 0.00 MiB (0 bytes)
2026-05-27T08:46:17,654216Z None/[69]JobWrapper INFO: Job Wrapper is starting the pre processing phase for job 69
Failed to execute job Path to executable /pbs/home/t/testcalc/DIRAC_1t6wameopilot/69/script.sh not found
Job failed in execution phase
Traceback (most recent call last):
File "/cvmfs/dirac.egi.eu/dirac/v9.0.18/Linux-x86_64/lib/python3.11/site-packages/DIRAC/WorkloadManagementSystem/JobWrapper/JobWrapperUtilities.py", line 209, in executePayload
raise JobWrapperError((result["Message"], result["Errno"]))
DIRAC.WorkloadManagementSystem.JobWrapper.JobWrapperUtilities.JobWrapperError: ('Path to executable /pbs/home/t/testcalc/DIRAC_1t6wameopilot/69/script.sh not found', 0)
2026-05-27T08:46:18,315698Z None/[69]JobWrapper INFO: CPU time left missing in sendJobAccounting
2026-05-27T08:46:18,316376Z None/[69]JobWrapper INFO: CPU time left in sendJobAccounting 0.34 0.04 0.00 0.00 1.57
2026-05-27T08:46:18,734923Z WorkloadManagement/JobAgent/InProcess WARN: Fail in payload execution
2026-05-27T08:46:18,735217Z WorkloadManagement/JobAgent/InProcess INFO: Exit status: 1
```

### Environment

_No response_

### Relevant Log Output

```shell

```

### Additional Context

_No response_