[CI] add xfails to hrtf_loading tests

Currently, the hrtf_loading tests report "PASS" for testcases that compare using the ROM hrtf against a different hrtf loaded from file. That is in a way correct, since non-BE for this cases is the expected and correct behaviour. However, the file comparison also reports warnings about delay differences which are visible despite the testcase passing. This confused at least me and lead to a review of the code since I suspected some bug. I think the reporting is confusing here and this MR changes the xfail conditions to actually report pytest.xfails.