MDL-81457 core: Do not mark tests as Incomplete when they are wrong

This check was marking a test as Incomplete if there was a bug in any
part of the test, rather than failing the test in such a way that the
test bug may be found.

https://docs.phpunit.de/en/9.6/incomplete-and-skipped-tests.html

enrol/tests/externallib_test.php

@@ -328,8 +328,9 @@ class externallib_test extends externallib_advanced_testcase {
                 $this->expectExceptionMessage($exception['message']);
             } else {
                 // Failed, only canview and exception are supported.
-                $this->markTestIncomplete('Incomplete, only canview and exception are supported');
+                throw new \coding_exception('Incomplete, only canview and exception are supported');
             }
+
             // Switch to the user and assign the role.
             $this->setUser(${$user});
             role_assign($roleid, $USER->id, $coursecontext);