src: fix compiler warning in async_wrap.cc

    ../src/async_wrap.cc: In function ‘uint16_t node::ToAsyncHooksType(v8::PromiseHookType)’:
    ../src/async_wrap.cc:313:1: error: control reaches end of non-void function [-Werror=return-type]
     }

Refs: #32891

PR-URL: #33322
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

src/async_wrap.cc

@@ -310,6 +310,7 @@ static uint16_t ToAsyncHooksType(PromiseHookType type) {
     case PromiseHookType::kAfter:   return AsyncHooks::kAfter;
     case PromiseHookType::kResolve: return AsyncHooks::kPromiseResolve;
   }
+  UNREACHABLE();
 }
 
 // Simplified JavaScript hook fast-path for when there is no destroy hook