[lldb] Add support for NoneType to decorator skipIfBuildType (llvm#145342)

Currently if cmake_build_type is None we error with `AttributeError:
'NoneType' object has no attribute 'lower'` if the decorator
skipIfBuildType is used. This fixes the issue by first checking that
cmake_build_type is not None.

Author: itf

lldb/packages/Python/lldbsuite/test/decorators.py

@@ -1155,6 +1155,7 @@ def skipIfBuildType(types: list[str]):
     """
     types = [name.lower() for name in types]
     return unittest.skipIf(
-        configuration.cmake_build_type.lower() in types,
+        configuration.cmake_build_type is not None
+        and configuration.cmake_build_type.lower() in types,
         "skip on {} build type(s)".format(", ".join(types)),
     )