[clang-tools-extra] [clang-tidy] Don't run use-nullptr check on objective-c code. (PR #141229)

[Sean McBride via cfe-commits]

seanm wrote:

Obj-C, being a superset of C, often has C code within it too, would this change mean that NULL -> nullptr won't be suggested at all?

Also, isn't Obj-C nil defined as nullptr?  I'm pretty sure it is in Obj-C++ at least.

https://github.com/llvm/llvm-project/pull/141229