fixup! Update RefTrace's garbage collection

Author: ajaust

python/segyio/trace.py

@@ -413,8 +413,10 @@ class RefTrace(Trace):
     modifications are written back to disk.
     """
 
-    # A truly internally held reference to a trace has count 2 (Python >=
-    # 3.14) and count 3 otherwise.
+    # If there are no external references to the data (so only internal
+    # references remain), the reference count is
+    # - 2 (Python >= 3.14)
+    # - 3 (Python < 3.14)
     _GARBAGE_THRESHOLD = 3 if sys.version_info < (3, 14) else 2
 
     def __init__(self, *args):