RT 75039: don't allow '=CUT' to terminate POD

Jae Gangemi's fix for https://rt.cpan.org/Public/Bug/Display.html?id=75039 with a test.

Note that the diff of t/ppi_token_pod.t is noisy because that file on master is out of synch with lib/PPI/Token/Pod.pm (at least with my inline2test version 2.213).