Update special_tokens_map.json

See comment: https://github.com/huggingface/transformers/issues/25036#issuecomment-1705349350

special_tokens_map.json

@@ -1,20 +1,20 @@
 {
   "bos_token": {
-    "content": "",
+    "content": "<s>",
     "lstrip": false,
     "normalized": true,
     "rstrip": false,
     "single_word": false
   },
   "eos_token": {
-    "content": "",
+    "content": "</s>",
     "lstrip": false,
     "normalized": true,
     "rstrip": false,
     "single_word": false
   },
   "unk_token": {
-    "content": "",
+    "content": "<unk>",
     "lstrip": false,
     "normalized": true,
     "rstrip": false,