Correctly apply rdoc prerequisite

It thought this didn't actually work but it seems it is necessary this way.
Unclear why `enhance` worked for the docs workflow but not for pages

Author: Earlopain

.github/workflows/github-pages.yml

@@ -1,6 +1,7 @@
 name: GitHub pages
 
 on:
+  pull_request:
   # Runs on pushes targeting the default branch
   push:
     branches:
@@ -23,7 +24,6 @@ concurrency:
 
 jobs:
   build:
-    if: github.repository == 'ruby/prism'
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -44,8 +44,6 @@ jobs:
       - name: Setup Pages
         id: pages
         uses: actions/configure-pages@v6
-      - name: Template source files
-        run: bundle exec rake templates
       - name: Build with RDoc
         run: bundle exec rake rdoc
       - name: Build with Doxygen
@@ -63,6 +61,7 @@ jobs:
           path: doc
 
   deploy:
+    if: github.repository == 'ruby/prism'
     environment:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}

rakelib/rdoc.rake

@@ -29,5 +29,5 @@ end
 %w[rdoc rerdoc rdoc:coverage].each do |name|
   # rdoc:coverage available in rdoc as a default gem since ruby 3.3 only
   next unless Rake::Task.task_defined?(name)
-  Rake::Task[name].enhance(["compile"])
+  Rake::Task[name].prerequisites.unshift("compile")
 end