ci: build docs on pull requests

.github/workflows/docs-build-deploy.yml

@@ -3,19 +3,26 @@ on:
   push:
     branches:
       - main
+  pull_request:
+    branches:
+      - main
+
 jobs:
   build-and-deploy:
     runs-on: ubuntu-latest
     permissions:
       contents: write
     steps:
-    - uses: actions/checkout@v3
-    - uses: actions/setup-python@v3
+    - uses: actions/checkout@v4
+    - uses: actions/setup-python@v5
+      with:
+        python-version: '3.12'
     - name: Install cats with documentation helpers
       run: python3 -m pip install '.[docs]'
     - name: Build sphinx docs
       run: make -C docs html
     - name: Deploy sphinx docs
+      if: github.ref == 'refs/heads/main'
       run: |
         git config user.name 'github-action'
         git config user.email 'github-action'