Generate and commit a missing test file

b969e1c7 added a reference to this file and a command to generate it into tests/mime-detection/list, but didn't commit the generated file itself. Now when test-mime fails for some other reason (e.g. after adding a failing test case), the following error message is printed: Could not open /path/to/shared-mime-info/tests/mime-detection/test-not-dtshd.txt

Presumably when the test file does not exist, the intended 'data' test does not run. The testing system should be improved to report such nonexistent file issues as test failures.