binary-search-tree tests are broken

[glennj]

Resulting from #408

For each test case, the tree sub is invoked for the input treeData. But because no attention is paid to the property, all the sortedData tests, which expect an arrayref, fail because the actual results are hashrefs.

[glennj]

Contrast this with the Clock test script: it accounts for the property. https://github.com/exercism/perl5/blob/main/exercises/practice/clock/clock.t