build(deps): bump ansys/actions from 5 to 6 (#415)

Bumps [ansys/actions](https://github.com/ansys/actions) from 5 to 6.
- [Release notes](https://github.com/ansys/actions/releases)
- [Commits](ansys/actions@v5...v6)

---
updated-dependencies:
- dependency-name: ansys/actions
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/testing-and-deployment.yml

@@ -32,20 +32,21 @@ jobs:
         uses: pyvista/setup-headless-display-action@v2
 
       - name: Build project documentation
-        uses: ansys/actions/doc-build@v5
+        uses: ansys/actions/doc-build@v6
         with:
           dependencies: 'pandoc'
           skip-dependencies-cache: true
           use-python-cache: false
           python-version: "3.10"
+          sphinxopts: "-j auto"
 
   doc-deploy-dev:
     name: Upload development documentation
     runs-on: ubuntu-latest
     needs: [doc_build]
     if: github.ref == 'refs/heads/main'
     steps:
-      - uses: ansys/actions/doc-deploy-dev@v5
+      - uses: ansys/actions/doc-deploy-dev@v6
         with:
           cname: ${{ env.DOCUMENTATION_CNAME }}
           token: ${{ secrets.GITHUB_TOKEN }}
@@ -268,7 +269,7 @@ jobs:
     needs: [Release]
     steps:
       - name: Deploy the stable documentation
-        uses: ansys/actions/doc-deploy-stable@v5
+        uses: ansys/actions/doc-deploy-stable@v6
         with:
           cname: ${{ env.DOCUMENTATION_CNAME }}
           token: ${{ secrets.GITHUB_TOKEN }}