fix line return (#531)

`len(data)` is the size of json object parsed from a line, which does
not represent the count of lines in the source file. This incorrectly
squashes most contents of the input file to the second line of the
output file.

---------

Co-authored-by: Yunfan Zhong <alanwake@in.ai>

berkeley-function-call-leaderboard/apply_function_credential_config.py

@@ -62,9 +62,9 @@ def process_file(input_file_path, output_file_path):
     with open(output_file_path, "w") as f:
         for i, modified_line in enumerate(modified_data):
             f.write(modified_line)
-            if i < len(modified_data) - 1:
-                f.write("\n")        
-            
+            if i < len(lines) - 1:
+                f.write("\n")
+
     print(f"All placeholders have been replaced for {input_file_path} 🦍.")