Update submissions.json

Ran on a notebook with:
```python
!pip install uv -qqq
!uv init
!uv add "triton<=3.2.0" "vllm<0.10.2" lighteval[vllm] -qqq
!uv run lighteval vllm "model_name=andregustavo/SmolLM3-Custom-SFT,dtype=float16" "lighteval|gsm8k|0|0" --push-to-hub --results-org andregustavo
```

This should work on hf jobs:
```python
hf jobs uv run \ # run a hf jobs job with uv
--flavor a10g-large \ # select the machine size
--with "triton<=3.2.0"
--with "vllm<0.10.2"
--with "lighteval[vllm]" \ # install lighteval with vllm dependencies
-s HF_TOKEN \ # share the huggingface write token
lighteval vllm "model_name=andregustavo/SmolLM3-Custom-SFT,dtype=float16" "lighteval|gsm8k|0|0" --push-to-hub --results-org <your-username>
```

submissions.json

@@ -6,6 +6,13 @@
             "chapter": "1",
             "submission_date": "2025-09-02",
             "results-dataset": "smol-course/details_HuggingFaceTB__SmolLM3-3B_private"
+        },
+        {
+            "username": "andregustavo",
+            "model_name": "SmolLM3-Custom-SFT",
+            "chapter": "1",
+            "submission_date": "2025-09-25",
+            "results-dataset": "andregustavo/details_andregustavo__SmolLM3-Custom-SFT_private"
         }
     ]
 }