update pr links (#12028)

- **Update PR links to use single-version**
- **Use string**
- **WHy won't it run**
- **Small docs change to =test**


<!-- readthedocs-preview docs start -->
---
:books: Documentation previews :books:

- User's documentation (`docs`):
https://docs--12028.org.readthedocs.build/en/12028/

<!-- readthedocs-preview docs end -->

<!-- readthedocs-preview dev start -->
- Developer's documentation (`dev`):
https://dev--12028.org.readthedocs.build/en/12028/

<!-- readthedocs-preview dev end -->

Author: ericholscher

.github/workflows/pr-preview-links.yaml

@@ -1,4 +1,4 @@
-name: Read the Docs Pull Request Preview
+name: Read the Docs PR Preview
 on:
   pull_request_target:
     types:
@@ -16,6 +16,7 @@ jobs:
       - uses: readthedocs/actions/preview@v1
         with:
           project-slug: "docs"
+          single-language: "true"
           message-template: |
             ---
             :books: Documentation previews :books:
@@ -25,5 +26,6 @@ jobs:
       - uses: readthedocs/actions/preview@v1
         with:
           project-slug: "dev"
+          single-language: "true"
           message-template: |
             - Developer's documentation (\`dev\`): {docs-pr-index-url}

docs/conf.py

@@ -17,6 +17,7 @@
 from multiproject.utils import get_project
 
 sys.path.append(os.path.abspath("_ext"))
+
 extensions = [
     "multiproject",
     "myst_parser",