fix: correct variable usage for language guessing in code block formatting

mineru/backend/vlm/vlm_middle_json_mkcontent.py

@@ -123,7 +123,8 @@ def mk_blocks_to_markdown(para_blocks, make_mode, formula_enable, table_enable,
             for block in para_block['blocks']:  # 2nd.拼code_body
                 if block['type'] == BlockType.CODE_BODY:
                     if sub_type == BlockType.CODE:
-                        para_text += f"```{para_block["guess_lang"]}\n{merge_para_with_text(block)}\n```"
+                        guess_lang = para_block["guess_lang"]
+                        para_text += f"```{guess_lang}\n{merge_para_with_text(block)}\n```"
                     elif sub_type == BlockType.ALGORITHM:
                         para_text += merge_para_with_text(block)