BUG: int dtype comparison goes wrong linelists.cdms on Windows with astropy 6.1

[bsipocz]

The CI failures seem to uncover some actual bugs. While running the tests locally on an OSX passes everything, I do see the bug if directly passing a non-string to parse_letternumber.

[bsipocz]

OK, diving into the code, the function is likely all good, but the conditional prior to its calling is wrong. I suspect astropy/astropy#16005 may be the cause, but I'm not certain as I cannot debug it locally (it only shows on windows).

I'll try a few things in a PR, and maybe will hit a solution that works.