Add 'when:always' to unit test report docs

- Adding an explanation about why you would want to have when:always in
  your unit test report job. This was previously omitted and should
clarify the yml definitions more.

- Resolves https://gitlab.com/gitlab-org/gitlab/-/issues/247849

doc/ci/unit_test_reports.md

@@ -81,6 +81,8 @@ merge request widget.
 
 To make the Unit test report output files browsable, include them with the
 [`artifacts:paths`](yaml/README.md#artifactspaths) keyword as well, as shown in the [Ruby example](#ruby-example).
+To upload the report even if the job fails (for example if the tests do not pass), use the [`artifacts:when:always`](yaml/README.md#artifactswhen)
+keyword.
 
 NOTE: **Note:**
 You cannot have multiple tests with the same name and class in your JUnit report format XML file.