Claude review: drm: xe: selftests: fix fence refcount leak in run_sanity_job()

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Patch Review

**Correctness: The code change is correct.**

The flow is:
1. Line 55: `fence = dma_fence_get(&job->drm.s_fence->finished);` — takes a reference
2. Line 56: `xe_sched_job_push(job);` — submits the job (job ownership transferred to scheduler)
3. Line 58: `sanity_fence_failed()` checks if the fence completed; if it failed, the original code returned without releasing the fence reference

The added `dma_fence_put(fence)` on the error path correctly balances the `dma_fence_get()`.

**Minor note on the commit message:** The commit message says "If the job submission fails, the function returns an error without calling dma_fence_put()". This is slightly misleading — the job submission (`xe_sched_job_push`) itself doesn't fail here. What happens is the fence *times out* (or is an error/NULL), and `sanity_fence_failed()` returns true. The leak occurs on the fence-wait failure path, not the job-submission failure path. The distinction matters because `xe_sched_job_push()` is a void function that always succeeds — the job is already pushed before the fence check.

**Fixes tag concern:** The `Fixes:` tag points to `dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")` which is the initial xe driver commit. While technically the buggy code was introduced there, this is a very broad Fixes tag. A more precise tag would reference whatever commit introduced or last modified `run_sanity_job()` into its current form. This matters because the `Cc: stable@vger.kernel.org` tag means this will be considered for backporting — using the initial driver commit as the Fixes tag could cause confusion about which stable branches need the fix.

**Stable backport concern:** This is a KUnit selftest fix — not a production code path. Tagging it `Cc: stable@vger.kernel.org` is questionable since the leak only occurs in test code during a fence timeout/failure scenario. Test-only fixes are generally not backported to stable kernels.

**Verdict:** The code change itself is correct and trivially safe. The metadata (commit message accuracy, Fixes tag precision, stable tag appropriateness) could be improved.

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