Update parserTests.txt to include combined link prefix/link trail tests.

The new test was added in https://gerrit.wikimedia.org/r/61617
and we fixed the exposed bugs in https://gerrit.wikimedia.org/r/61691

The new test fails html2html and html2wt, like all the link tests do.
(The HTML in the parserTests is missing the rel="mw:WikiLink" on the
<a> tag which WikitextSerializer expects.)

Change-Id: I6332e5bcb29cde13437e1cdddb06b23e87c745da