[PATCH 2/3] testsuite: Update tests for 'xfmemopen' use

[Maciej W. Rozycki]

On Mon, 25 Aug 2025, Florian Weimer wrote:

> > Convert tests to use 'xfmemopen' rather than open-coding error checks 
> > with 'fmemopen' or plain missing them, where 'fmemopen' itself is not 
> > the scope of testing.  Leave 'fmemopen' tests alone.
> 
> Looks okay.

 Committed now, thanks for your review.

  Maciej