glthread: apply the thread scheduling policy when a batch executes synchronously

before this, when no batch was executed asynchronously, the policy wasn't
applied

Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27247>

src/mesa/main/glthread.c

@@ -401,6 +401,8 @@ _mesa_glthread_finish(struct gl_context *ctx)
       synced = true;
    }
 
+   glthread_apply_thread_sched_policy(ctx, false);
+
    if (glthread->used) {
       /* Mark the end of the batch, but don't increment "used". */
       struct marshal_cmd_base *last =