chore: only build doc once in the CI

I've chosen to keep the one in the "lint" step, instead of a
dedicated step, so to prevent one more container to be built at
each run (did I say "to save trees" ?) :p

.github/workflows/test-docs.yml

@@ -63,7 +63,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: '3.11'
+          python-version: '3.12'
       - name: Install dependencies
         run: |
           python3 -m pip install -e .[test,dev]
@@ -74,18 +74,3 @@ jobs:
 
       - name: Run Docs
         run: make docs
-
-  docs:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - name: Set up Python
-        uses: actions/setup-python@v5
-        with:
-          python-version: '3.11'
-      - name: Install dependencies
-        run: |
-          python3 -m pip install -r docs/requirements.txt
-
-      - name: Run Docs
-        run: mkdocs build