[lldb] Fix Python test formatting (NFC)

All Python files in the LLVM repository were reformatted with Black [1].
Files inside the LLDB subproject were reformatted in 2238dcc3. This
patch updates a handful of tests that were added or modified since then
and weren't formatted with Black.

[1] https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style/68257