[clangd][NFC] Silence some buildbot warnings after 0250b053

https://reviews.llvm.org/D94554 introduced code which wont compile with some build flags due to a field having the same identifier as a type.

clang-tools-extra/clangd/DraftStore.h:55:11: error: declaration of ‘clang::clangd::DraftStore::Draft clang::clangd::DraftStore::DraftAndTime::Draft’ changes meaning of ‘Draft’ [-fpermissive]
   55 |     Draft Draft;
      |           ^~~~~
clang-tools-extra/clangd/DraftStore.h:30:10: note: ‘Draft’ declared here as ‘struct clang::clangd::DraftStore::Draft’
   30 |   struct Draft {
         |          ^~~~~