Remove matrix in CI tests (it's just 1 job)

.github/workflows/django.yml

@@ -14,11 +14,6 @@ jobs:
   build-ubuntu:
 
     runs-on: ubuntu-latest
-    strategy:
-      max-parallel: 4
-      matrix:
-        python-version: [3.9]
-        node-version: [12.x]
 
     services:
       postgres:
@@ -55,14 +50,14 @@ jobs:
         key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
         restore-keys: |
           ${{ runner.os }}-pip-
-    - name: Set up Python ${{ matrix.python-version }}
+    - name: Set up Python
       uses: actions/setup-python@v2
       with:
-        python-version: ${{ matrix.python-version }}
-    - name: Use Node.js ${{ matrix.node-version }}
+        python-version: 3.9
+    - name: Set up Node.js
       uses: actions/setup-node@v1
       with:
-        node-version: ${{ matrix.node-version }}
+        node-version: 12.x
     - name: Install Dependencies
       run: |
         python -m pip install --upgrade pip