Investigate tbb-test for #23104 (line height compensation)

After the changes from tor-browser#30832 (closed) we set layout.css.line-height.normal-as-resolved-value.enabled = false in order to measure the line-height correctly for the arabic test case (see tor-browser#30832 (comment 2664115)). We should try to investigate and possibly fix the test case so that we don't have to set that pref.