Unqualified LoadPackage in tst/testbugfix/2023-10-18-SetDimension.tst

[james-d-mitchell]

The package fining is loaded in the file testbugfix/2023-10-18-SetDimension.tst which causes this test to fail when fining isn't available, such as in:

https://github.com/semigroups/Semigroups/actions/runs/7423583401/job/20201324551?pr=970

This is in the master branch.

It doesn't seem very sensible to have tests in the main GAP repo that rely on non-mandatory packages being available, and this is the only instance in the tests (at least according to a quick grep). Everywhere else there's an if LoadPackage("blah") <> fail then in the test file, seems like it'd be a good idea to that here too.