[clang] [Clang][Test] Fix -Wctad-maybe-unsupported in OperatorNewDeletePointersExtractorTest.cpp (PR #209012)

[Wenju He via cfe-commits]

wenju-he wrote:

> BTW why is it not intended to support CTAD?

Updated commit message:
std::set{*PtrId} does implicitly deduce to std::set<EntityId>, but it is not explicit or user-defined CATD guide. Opt-in warning -Wctad-maybe-unsupported flags it as maybe unsafe and unintended. The warning is enabled at https://github.com/llvm/llvm-project/blob/9083925dadb4/llvm/cmake/modules/HandleLLVMOptions.cmake#L977

https://github.com/llvm/llvm-project/pull/209012