Fix PNNX debug filename (#3687)

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

ultralytics/yolo/engine/exporter.py

@@ -445,8 +445,8 @@ class Exporter:
         f.mkdir(exist_ok=True)  # make ncnn_model directory
         LOGGER.info(f"{prefix} running '{' '.join(cmd)}'")
         subprocess.run(cmd, check=True)
-        for f in 'debug.bin', 'debug.param', 'debug2.bin', 'debug2.param':  # remove debug files
-            Path(f).unlink(missing_ok=True)
+        for f_debug in 'debug.bin', 'debug.param', 'debug2.bin', 'debug2.param':  # remove debug files
+            Path(f_debug).unlink(missing_ok=True)
 
         yaml_save(f / 'metadata.yaml', self.metadata)  # add metadata.yaml
         return str(f), None