[clangd] Fix typo in GUARDED_BY()

[ilya-biryukov]

LGTM

clang-tools-extra/clangd/TUScheduler.cpp

private:
   // FIXME: rename it to better fix the current usage, we also use it to guard
   // emitting TUStatus.
   /// Guards a critical section for running the diagnostics callbacks.
   std::mutex DiagsMu;
   // Used to prevent remove document + leading to out-of-order diagnostics:
   // The lifetime of the old/new ASTWorkers will overlap, but their handles
   // don't. When the old handle is destroyed, the old worker will stop reporting
   // diagnostics.
-  bool ReportDiagnostics = true; /* GUARDED_BY(DiagMu) */
+  bool ReportDiagnostics = true; /* GUARDED_BY(DiagsMu) */
 };
 
 /// A smart-pointer-like class that points to an active ASTWorker.
 /// In destructor, signals to the underlying ASTWorker that no new requests will
 /// be sent and the processing loop may exit (after running all pending
 /// requests).
 class ASTWorkerHandle {
   friend class ASTWorker;