DEV: Double timeout for spec in spec/defer_spec.rb (#35368)

We get the following failure from time to time on CI. Just double the
timeout for now.

```
Failure/Error: expect(x).to eq(3)

  expected: 3
       got: 2

  (compared using ==)

./spec/lib/scheduler/defer_spec.rb:95:in `block (2 levels) in <main>'
./spec/rails_helper.rb:704:in `block (3 levels) in <top (required)>'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/benchmark-0.4.1/lib/benchmark.rb:305:in `measure'
./spec/rails_helper.rb:704:in `block (2 levels) in <top (required)>'
./spec/rails_helper.rb:662:in `block (3 levels) in <top (required)>'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/timeout-0.4.3/lib/timeout.rb:185:in `block in timeout'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/timeout-0.4.3/lib/timeout.rb:192:in `timeout'
./spec/rails_helper.rb:652:in `block (2 levels) in <top (required)>'
./spec/rails_helper.rb:609:in `block (2 levels) in <top (required)>'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/webmock-3.25.1/lib/webmock/rspec.rb:39:in `block (2 levels) in <top (required)>'
```

spec/lib/scheduler/defer_spec.rb

@@ -90,7 +90,7 @@ RSpec.describe Scheduler::Defer do
 
     @defer.later { x = 3 }
 
-    wait_for(1000) { x == 3 }
+    wait_for(2000) { x == 3 }
 
     expect(x).to eq(3)
   end