Update GitHub actions to latest version

Also:
 - Change cache to pipenv modules
 - Remove asgiref from Pipfile
 - Make action case consistent

.github/workflows/django.yml

@@ -30,9 +30,19 @@ jobs:
       GITHUB_CI: true # Just 'CI' clashes with Render
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
+    - name: Set up Python
+      # The actions/cache step below uses this id to get the exact python version
+      id: setup-python
+      uses: actions/setup-python@v3
+      with:
+        python-version: 3.9
+    - name: Set up Node.js
+      uses: actions/setup-node@v3
+      with:
+        node-version: 12.x
     - name: Cache node modules
-      uses: actions/cache@v2
+      uses: actions/cache@v3
       env:
         cache-name: cache-node-modules
       with:
@@ -43,44 +53,34 @@ jobs:
           ${{ runner.os }}-build-${{ env.cache-name }}-
           ${{ runner.os }}-build-
           ${{ runner.os }}-
-    - name: Cache pip modules
-      uses: actions/cache@v2
+    - name: Cache pipenv modules
+      uses: actions/cache@v3
       with:
-        path: ~/.cache/pip
-        key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
-        restore-keys: |
-          ${{ runner.os }}-pip-
-    - name: Set up Python
-      uses: actions/setup-python@v2
-      with:
-        python-version: 3.9
-    - name: Set up Node.js
-      uses: actions/setup-node@v1
-      with:
-        node-version: 12.x
-    - name: Install Dependencies
+        path: ~/.local/share/virtualenvs
+        key: ${{ runner.os }}-python-${{ steps.setup-python.outputs.python-version }}-pipenv-${{ hashFiles('Pipfile.lock') }}
+    - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
         python -m pip install pipenv
         pipenv install --system --dev
         npm ci
-    - name: Run Linting
+    - name: Run linting
       run: npm run lint
-    - name: Run Build and Collect
+    - name: Run build and collect
       run: |
         npm run build
         python ./tabbycat/manage.py collectstatic --noinput -v 0
-    - name: Run Migrations
+    - name: Run migrations
       run: python ./tabbycat/manage.py migrate
-    - name: Run Tests
+    - name: Run tests
       run: python tabbycat/manage.py test -v 2 --exclude-tag=selenium
 
   build-docker-dev:
 
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           fetch-depth: 1
       - name: Build Docker image (dev)
@@ -91,7 +91,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           fetch-depth: 1
       - name: Build Docker image (prod)