Skip sequel for truffleruby

<internal:core> core/kernel.rb:282:in `require_relative': /home/runner/.rubies/truffleruby-head/lib/gems/gems/sequel-5.68.0/lib/sequel/dataset/query.rb:90: Invalid return in class/module body (SyntaxError)
	from /home/runner/.rubies/truffleruby-head/lib/gems/gems/sequel-5.68.0/lib/sequel/dataset.rb:47:in `<module:Sequel>'
	from /home/runner/.rubies/truffleruby-head/lib/gems/gems/sequel-5.68.0/lib/sequel/dataset.rb:3:in `<top (required)>'
	from <internal:core> core/kernel.rb:292:in `require_relative'
	from /home/runner/.rubies/truffleruby-head/lib/gems/gems/sequel-5.68.0/lib/sequel/core.rb:429:in `<module:Sequel>'
	from /home/runner/.rubies/truffleruby-head/lib/gems/gems/sequel-5.68.0/lib/sequel/core.rb:27:in `<top (required)>'
	from <internal:core> core/kernel.rb:292:in `require_relative'
	from /home/runner/.rubies/truffleruby-head/lib/gems/gems/sequel-5.68.0/lib/sequel/model.rb:3:in `<top (required)>'
	from <internal:core> core/kernel.rb:292:in `require_relative'
	from /home/runner/.rubies/truffleruby-head/lib/gems/gems/sequel-5.68.0/lib/sequel.rb:3:in `<top (required)>'
	from <internal:core> core/kernel.rb:229:in `gem_original_require'
	from <internal:/home/runner/.rubies/truffleruby-head/lib/mri/rubygems/core_ext/kernel_require.rb>:38:in `require'
	from /home/runner/work/yjit-bench/yjit-bench/benchmarks/sequel/benchmark.rb:7:in `<main>'

Author: k0kubun

.github/workflows/test.yml

@@ -16,7 +16,7 @@ jobs:
           - ruby: ruby
           - ruby: head
           - ruby: truffleruby-head
-            skip: protoboeuf-encode
+            skip: protoboeuf-encode sequel
     if: ${{ github.event_name != 'schedule' || github.repository == 'Shopify/yjit-bench' }}
     steps:
       - uses: actions/checkout@v3