Fix incorrect string formatting in barrier timeout exceptions (#27149)

Signed-off-by: Yongtao Huang <yongtaoh2022@gmail.com>

vllm/distributed/utils.py

@@ -277,7 +277,7 @@ class StatelessProcessGroup:
             # Check for timeout
             cur_time = time.time()
             if cur_time - start_time > timeout:
-                raise RuntimeError("Barrier timed out after %f seconds", timeout)
+                raise RuntimeError(f"Barrier timed out after {timeout:.2f} seconds")
 
             # Check for each process
             for i in range(self.world_size):
@@ -324,7 +324,9 @@ class StatelessProcessGroup:
         while len(processes_departed) < self.world_size:
             # Check for timeout
             if time.time() - start_time > timeout:
-                raise RuntimeError("Barrier departure timed out after %f s", timeout)
+                raise RuntimeError(
+                    f"Barrier departure timed out after {timeout:.2f} seconds"
+                )
 
             # Check for each process
             for i in range(self.world_size):