When debug info categories were set for a test method with the
`@add_test_categories` decorator, they were all added to its
"categories" attribute. If some of these categories were not supported,
`LLDBTestResult.startTest()` skipped all variants of the test method.
For example, the tests in `TestWithLimitDebugInfo.py` use the categories
`dwarf` and `dwo`. However, since `dwo` is not supported on Windows, all
the tests in this file were skipped, even though the tests for `dwarf`
could be run.