fix thread_pool.warm returning without spawning new threads

src/thread_pool.zig

@@ -422,15 +422,17 @@ pub fn warm(self: *ThreadPool, count: u14) void {
     while (sync.spawned < to_spawn) {
         var new_sync = sync;
         new_sync.spawned += 1;
-        sync = @as(Sync, @bitCast(self.sync.cmpxchgWeak(
+        sync = @bitCast(self.sync.cmpxchgWeak(
             @as(u32, @bitCast(sync)),
             @as(u32, @bitCast(new_sync)),
             .release,
             .monotonic,
-        ) orelse break));
-        const spawn_config = std.Thread.SpawnConfig{ .stack_size = default_thread_stack_size };
-        const thread = std.Thread.spawn(spawn_config, Thread.run, .{self}) catch return self.unregister(null);
-        thread.detach();
+        ) orelse blk: {
+            const spawn_config = std.Thread.SpawnConfig{ .stack_size = self.stack_size };
+            const thread = std.Thread.spawn(spawn_config, Thread.run, .{self}) catch return self.unregister(null);
+            thread.detach();
+            break :blk @as(u32, @bitCast(new_sync));
+        });
     }
 }