Blacklist LinkHovered tests on Linuxes after fix did not work

6252f023

 tried fixing
these autotests. As it evidently didn't work, we bring
the blacklisting back.

Task-number: QTBUG-55870
Change-Id: I12dc54a81cc25f743f1b37e321a6524ba6b5915c
Reviewed-by: Peter Varga <pvarga@inf.u-szeged.hu>