ci: Enable YJIT and separated older builds

Author: toshimaru

.github/workflows/ci.yml

@@ -48,11 +48,15 @@ jobs:
   doc-build-others:
     runs-on: ubuntu-latest
     name: Rails Doc Build (older versions)
+    env:
+      RUBY_YJIT_ENABLE: ${{ matrix.yjit-enabled }}
     strategy:
       matrix:
         include:
           - ruby-version: 2.7
-            build-rails-versions: "5.2,6.0,6.1"
+            build-rails-versions: "5.2"
+          - ruby-version: 3.0
+            build-rails-versions: "6.0,6.1"
           - ruby-version: 3.3
             build-rails-versions: "7.0,7.1,7.2"
     steps: