[clang] [clang-tools-extra] [clangd] Fix: exclude insertions at end of CursorPlaceholder in formatting (PR #87746)

[via cfe-commits]

roife wrote:

I'm not sure why the test is showing as failed since all tests of clangd have passed; I didn't find any failed tests in the log.

https://github.com/llvm/llvm-project/pull/87746