[grpo] check liger & sp (#4734)

Author: hjh0119

swift/llm/argument/rlhf_args.py

@@ -259,6 +259,8 @@ def _check_grpo(self):
             assert trl_version >= version.parse('0.18')
             if self.delta is not None:
                 raise ValueError('Liger loss does not support two-sided GRPO loss yet.')
+            if self.sequence_parallel_size > 1:
+                raise ValueError('Liger loss does not support sequence parallel yet.')
             from trl.import_utils import is_liger_kernel_available
             assert is_liger_kernel_available(), (
                 'Please install/update liger-kernel by running: pip install -U liger-kernel')