Force gc.collect to work around regression caused by vllm-project#21146

Author: micah-wil

vllm/v1/worker/gpu_model_runner.py

@@ -2637,6 +2637,7 @@ def freeze_gc():
             finally:
                 if should_freeze:
                     gc.unfreeze()
+                    gc.collect()
 
         # Trigger CUDA graph capture for specific shapes.
         # Capture the large shapes first so that the smaller shapes