windows cannot run the GBTOnline() test

[teuben]

Describe the bug
Under Windows it seems the GBTOnline() is not working correctly. I emulate a bigger file by copying a bigger file onto the first file, and thus the sdf should see more scans....

Arguably we won't see GBTOnline() being used on windows , but it's useful to figure out what windows is doing here

How to Reproduce
In test_online() the 2nd copyfile fails on windows

       shutil.copyfile(f1, o1)
        sdf = gbtfitsload.GBTOnline()
        s = sdf.summary()
        n = len(sdf._index)
        assert n == 4
       shutil.copyfile(f2, o1)

Environment

• Dysh version: 0.4.0pre
• Python version: 3.11
• OS: windows