ci: Run make docs on PRs

.github/workflows/prepare-docs.yml

@@ -1,12 +1,32 @@
 name: Build docs artifact with Verific
 
-on: push
+on: [push, pull_request]
 
 jobs:
+  check_docs_rebuild:
+    runs-on: ubuntu-latest
+    outputs:
+      skip_check: ${{ steps.skip_check.outputs.should_skip }}
+      docs_export: ${{ steps.docs_var.outputs.docs_export }}
+    env:
+      docs_export: ${{ github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/heads/docs-preview') || startsWith(github.ref, 'refs/tags/') }}
+    steps:
+      - id: skip_check
+        uses: fkirc/skip-duplicate-actions@v5
+        with:
+          paths_ignore: '["**/README.md"]'
+          # don't cancel in case we're updating docs
+          cancel_others: 'false'
+          # only run on push *or* pull_request, not both
+          concurrent_skipping: ${{ env.docs_export && 'never' || 'same_content_newer'}}
+      - id: docs_var
+        run: echo "docs_export=${{ env.docs_export }}" >> $GITHUB_OUTPUT
+
   prepare-docs:
     # docs builds are needed for anything on main, any tagged versions, and any tag
     # or branch starting with docs-preview
-    if: ${{ github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/heads/docs-preview') || startsWith(github.ref, 'refs/tags/') }}
+    needs: check_docs_rebuild
+    if: ${{ needs.check_docs_rebuild.outputs.should_skip != 'true' }}
     runs-on: [self-hosted, linux, x64, fast]
     steps:
       - name: Checkout Yosys
@@ -45,6 +65,7 @@ jobs:
             docs/source/code_examples
 
       - name: Trigger RTDs build
+        if: ${{ needs.check_docs_rebuild.outputs.docs_export == 'true' }}
         uses: dfm/rtds-action@v1.1.0
         with:
           webhook_url: ${{ secrets.RTDS_WEBHOOK_URL }}