Deploy sim to GH pages for tags

Maintain ability to manually dispatch workflow.

Author: microbit-robert

.github/workflows/build-simx.yml

@@ -29,7 +29,7 @@ jobs:
         working-directory: simx
       - name: github pages
         uses: peaceiris/actions-gh-pages@v3
-        if: ${{ github.ref == 'refs/heads/main' }}
+        if: ${{ startsWith(github.ref, 'refs/tags/v') || github.ref == 'refs/heads/main' }}
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./simx/dist