Use dirhtml builder for docs instead of html

This fixes canonical URLs ending in `/index.html` by generating
directory-style URLs (`/`), which avoids the Google Search Console
indexing warning: "Alternate page with proper canonical tag."

Author: pavelacamposp

.github/workflows/docs.yml

@@ -32,13 +32,13 @@ jobs:
 
     - name: Build docs
       working-directory: ./docs
-      run: make html
+      run: make dirhtml
 
     - name: Upload docs artifact
       uses: actions/upload-artifact@v4
       with:
-        name: docs-html
-        path: ./docs/build/html
+        name: docs-dirhtml
+        path: ./docs/build/dirhtml
 
   deploy_docs:
     runs-on: ubuntu-latest
@@ -47,11 +47,11 @@ jobs:
     - name: Download artifacts
       uses: actions/download-artifact@v4
       with:
-        name: docs-html
-        path: ./docs/build/html
+        name: docs-dirhtml
+        path: ./docs/build/dirhtml
 
     - name: Deploy to gh-pages
       uses: peaceiris/actions-gh-pages@v4
       with:
         github_token: ${{ secrets.GITHUB_TOKEN }}
-        publish_dir: ./docs/build/html
+        publish_dir: ./docs/build/dirhtml