Simplify CI config

.github/workflows/lint.yml

@@ -6,9 +6,6 @@ jobs:
   build:
 
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        python-version: ["3.8"]
 
     name: Python ${{ matrix.python-version }}
 
@@ -31,18 +28,18 @@ jobs:
         restore-keys: |
           lint-pre-commit-
 
-    - name: Set up Python ${{ matrix.python-version }}
+    - name: Set up Python
       uses: actions/setup-python@v2
       with:
-        python-version: ${{ matrix.python-version }}
+        python-version: 3.8
 
     - name: Build system information
       run: python .github/workflows/system-info.py
 
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pip
-        python -m pip install --upgrade tox
+        python -m pip install -U pip
+        python -m pip install -U tox
 
     - name: Lint
       run: tox -e lint