I have left a comment on that ticket as well as elsewhere on GitHub
where there is a related report and proposed fix.
In the meantime I suggest using cpanm --force to install Tkx. This will
ignore the single test failure that prevents installation. The failing
test is merely for intentionally generating an error message, which
still works but no longer produces the exact message that was hardcoded
into the test long ago.
Hope this helps
Christopher A. Chavez