Better explain conditional cleanup in test_base_object

This expands the comment added in 41fac85 (gitpython-developers#1770) to make more
clear that this particular cleanup is deliberately done only when
the operation was successful (and why).

test/test_base.py

@@ -72,7 +72,10 @@ def test_base_object(self):
                 self.assertEqual(item, item.stream_data(tmpfile))
                 tmpfile.seek(0)
                 self.assertEqual(tmpfile.read(), data)
-            os.remove(tmpfile.name)  # Do it this way so we can inspect the file on failure.
+
+            # Remove the file this way, instead of with a context manager or "finally",
+            # so it is only removed on success, and we can inspect the file on failure.
+            os.remove(tmpfile.name)
         # END for each object type to create
 
         # Each has a unique sha.