Fix RT#75376: finding the 'cover' script in t/testcover.pm
Fix RT#75376: finding the 'cover' script in t/testcover.pm

RT#75376: t/testcover.pm does not correctly find the 'cover' script in
an environment where it is not installed in the Perl system directories
but instead elsewhere in $ENV{PATH}.
This patch fixes this by using File::Which.

captin411/devel-cover-report-clover,pine613/devel-cover-report-clover,pine613/devel-cover-report-clover