[lldb][swift] Re-enable TestSwiftUnknownSelf

[Teemperor]

This was skipped as it apparently regressed while the swiftTests were
unintentionally disabled. I can't reproduce this failure anymore and it
seems to consistently pass, so let's re-enable it.

[Teemperor]

@swift-ci test

[Teemperor]

@swift-ci test

[Teemperor]

12:31:29 Ran 4 tests in 25.161s
12:31:29 
12:31:29 RESULT: PASSED (2 passes, 0 failures, 0 errors, 2 skipped, 0 expected failures, 0 unexpected successes)
12:31:29 libc++abi.dylib: terminating with uncaught exception of type std::__1::system_error: recursive_mutex lock failed: Invalid argument
12:31:29 
12:31:29 --

same error as in the bindings update but in another test

[Teemperor]

@swift-ci test