Update build-doc.yml

Change checkout@master to checkout@v2

.github/workflows/build-doc.yml

@@ -12,8 +12,10 @@ on:
 
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch:
+
 permissions:
   contents: write
+
 # A workflow run is made up of one or more jobs that can run sequentially or in parallel
 jobs:
   # This workflow contains a single job called "build"
@@ -24,14 +26,15 @@ jobs:
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
       - name: Checkout
-        uses: actions/checkout@master
+        uses: actions/checkout@v2
         with:
           fetch-depth: 0
-      - uses: actions/setup-python@v4
+      - name: Set up Python 3.9
+        uses: actions/setup-python@v4
         with:
-          python-version: 3.9
+          python-version: "3.9"
       - uses: abatilo/actions-poetry@v2
-      - name: install
+      - name: Install
         run: poetry install --extras docs
       - name: Build documentation
         run: |