pyproject: split lint and doc dependencies

This allows a subset of dependencies to be installed if needed and
allows sharing requirements with readthedocs.

.github/workflows/build.yml

@@ -20,19 +20,11 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-20.04
-    strategy:
-      matrix:
-        python-version: [3.8, 3.9]
-
+    runs-on: ubuntu-22.04
     steps:
     - uses: actions/checkout@v3
       with:
         submodules: recursive
-    - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v1
-      with:
-        python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
         pip install poetry