backwards compatible check

tfs/writer.py

@@ -122,7 +122,8 @@ def write_tfs(
     data_frame.columns = data_frame.columns.astype(str)  
 
     # Only perform validation if asked (validation is OFF by default)
-    if validate is not None:  # validation function checks for valid values
+    # We also check for False as it was the way to skip it in tfs-pandas 3.x
+    if validate is not None and validate is not False:  # validation function will check for valid values
         validate_frame(
             data_frame,
             info_str=f"to be written in {tfs_file_path.absolute()}",