Update EOS token to match 7B equivalent.

Maintain consistency with https://huggingface.co/unsloth/Qwen2.5-Coder-7B/blob/main/special_tokens_map.json. I found out that this was set incorrectly when I tried to distill Unsloth's 7B into 3B and it never stopped generating. Crazy bug.

special_tokens_map.json

@@ -15,7 +15,7 @@
     "<|video_pad|>"
   ],
   "eos_token": {
-    "content": "<|im_end|>",
+    "content": "<|endoftext|>",
     "lstrip": false,
     "normalized": false,
     "rstrip": false,