Test on head given 4.0 isn't showing up

As of writing this[1] does not include 4.0
[1] https://cache.ruby-lang.org/pub/misc/ci_versions/cruby.json

Author: jbourassa

.github/workflows/ci.yml

@@ -20,11 +20,6 @@ jobs:
     steps:
       - id: fetch
         uses: oxidize-rb/actions/fetch-ci-data@1.4.3
-        with:
-          stable-ruby-versions: |
-              # See https://github.com/bytecodealliance/wasmtime-rb/issues/286
-              # for details.
-              exclude: [head]
 
   ci:
     runs-on: ${{ matrix.os }}