[clang] [libcxx] [clang] remove extra space in warn_atomic_op_oversized (NFC) (PR #110955)

[Louis Dionne via cfe-commits]

ldionne wrote:

I'm not a codeowner for Clang, but in this case I think the change is simple enough that this is good to go.

https://github.com/llvm/llvm-project/pull/110955