Upgrade pip before installing any packages, in case the VM is behind.

Just avoids a warning.

.github/workflows/linting.yml

@@ -1,23 +1,24 @@
-name: Linting
-
-on: [push, pull_request]
-
-jobs:
-  lint:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-
-      - name: Setup Python
-        uses: actions/setup-python@v2
-        with:
-          python-version: 3.9
-
-      - name: Install dependencies
-        run: |
-          pip install -r requirements-first.txt
-          pip install --pre -r requirements-dev.txt
-      - name: isort
-        run: isort --recursive --diff .
-      - name: Black
-        run: black --check .
+name: Linting
+
+on: [push, pull_request]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Setup Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.9
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements-first.txt
+          pip install -r requirements-dev.txt
+      - name: isort
+        run: isort --recursive --diff .
+      - name: Black
+        run: black --check .