[lldb] Fix language label in ObjC Language unittest

The recently added ObjC Language unittest, InvalidMethondNameParsing, currently has CPlusPlusLanguage as its language label (see https://reviews.llvm.org/D149804). There is already a test with the same name and same language label in the C++ Language unittests, so this creates a name conflict. This patch corrects the language label on the ObjC test.

Differential Revision: https://reviews.llvm.org/D150019