[clang] Fix the double space and double attribute printing of the final keyword. (PR #88600)

[Kim Gräsman via cfe-commits]

kimgr wrote:

Current PR passes all my tests, both Clang (`ninja ASTTests`), Clangd (`ninja ClangdTests`) and IWYU end-to-end tests -- thanks!

https://github.com/llvm/llvm-project/pull/88600