🖋️ Fix warning message formatting in KTOTrainer (huggingface#2394)

Author: qgallouedec

trl/trainer/kto_trainer.py

@@ -729,12 +729,12 @@ def make_inputs_require_grad(module, input, output):
 
                 if not (des_weight_in_range or und_weight_in_range):
                     warnings.warn(
-                        f"""
-                        You have different amounts of desirable/positive and undesirable/negative examples but the
-                        weights on the desirable and undesirable losses don't seem to be in an ideal range. Based
-                        on your data, we recommend EITHER desirable_weight in [{des_weight_lower_bound}, {des_weight_upper_bound}]
-                        or undesirable_weight in [{und_weight_lower_bound}, {und_weight_upper_bound}] (but NOT BOTH).
-                        See the documentation on how to optimally set these weights.""",
+                        "You have different amounts of desirable/positive and undesirable/negative examples but the "
+                        "weights on the desirable and undesirable losses don't seem to be in an ideal range. Based "
+                        f"on your data, we recommend EITHER "
+                        f"desirable_weight in [{des_weight_lower_bound}, {des_weight_upper_bound}] or "
+                        f"undesirable_weight in [{und_weight_lower_bound}, {und_weight_upper_bound}] (but NOT BOTH). "
+                        "See the documentation on how to optimally set these weights.",
                         UserWarning,
                     )