Load nunit test results *results.xml and confirm tests are running

Now that Unity is activated inside docker and that builds are being created correctly, we need to confirm that tests are really running for the project.

By passing -testResults ./results.xml to unity command line argument, it should generate nunit test results. See https://gitlab.com/gableroux/unity3d-gitlab-ci-example/blob/cce6670a/.gitlab-ci.yml#L13

The -testResults command line argument is currently passed, but as shown by the following CI job: https://gitlab.com/gableroux/unity3d-gitlab-ci-example/-/jobs/67933950

WARNING: ./editmode-results.xml: no matching files

test results doesn't seem to be generated. In fact, project may even not run the tests effectively.