[lldb][LocateModuleCallback] Fix LocateModuleCallbackTest

D153734 forgot to call `Platform::SetHostPlatform` before
`Debugger::CreateInstance`. Copy similar code.
https://github.com/llvm/llvm-project/blob/5007c78ce0936824972ec6ba3cfa598192087ee1/lldb/unittests/Expression/DWARFExpressionTest.cpp#L371-L374

Differential Revision: https://reviews.llvm.org/D155135