Add integration tests

[ErikSchierboom]

There should be tests to verify the test runner behavior from an input/output perspective. The best option is probably to mimic what other tracks are doing, and having a tests directory with some golden tests (see https://github.com/exercism/prolog-test-runner/tree/main/tests) and then having a bin/run-tests.sh and [bin/run-tests-in-docker.sh](https://github.com/exercism/prolog-test-runner/blob/main/bin/run-tests-in-docker.sh] script files. These are then used in a CI workflow.

[senekor]

I think this was completed with #41, right?

[ErikSchierboom]

Correct