some tests fail if kpsewhich prints to STDERR

[xworld21]

Splitting out the report in https://github.com/brucemiller/LaTeXML/issues/2441?notification_referrer_id=NT_kwDOAB3z6bMxMzU4MTA3MzA5MjoxOTYyOTg1#issuecomment-2508957714: if kpsewhich emits error messages for whichever reason, some tests fail because they expect output 'No obvious problem'. This may happen on Windows, where MikTeX's kpsewhich occasionally complains about permissions.

I suggest that the tests only check the last line of the standard error.