move build docs to only one python version

Signed-off-by: Michele Dolfi <[email protected]>

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ env:
   POETRY_VIRTUALENVS_CREATE: false
 
 jobs:
-  test-style-and-build-docs:
+  test-styles:
     runs-on: ubuntu-latest
     strategy:
       matrix:
@@ -31,5 +31,18 @@ jobs:
         run: poetry install
       - name: Run styling check
         run: pre-commit run --all-files
+  build-docs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install poetry
+        run: pip install poetry
+      - uses: actions/setup-python@v4
+        with:
+          python-version: 3.x
+          cache: 'pip'
+          cache-dependency-path: 'poetry.lock'
+      - name: Install dependencies
+        run: poetry install
       - name: Build docs
         run: mkdocs build --verbose --clean