build: use pinned Django version for tests

.github/workflows/unit-tests.yml

@@ -13,7 +13,9 @@ jobs:
     strategy:
       matrix:
         python-version: ['3.8']
-        django-version: ["3.2"]
+        django-version:
+          - "pinned"
+          #- "4.0"
         shard_name: [
             "lms-1",
             "lms-2",
@@ -37,7 +39,9 @@ jobs:
     steps:
       - name: sync directory owner
         run: sudo chown runner:runner -R .*
-      - uses: actions/checkout@v2
+
+      - name: checkout repo
+        uses: actions/checkout@v2
 
       # This gives Mongo several chances to start. We started getting flakiness
       # around 2022-02-15 wherein the start command would sometimes exit with:
@@ -58,7 +62,15 @@ jobs:
         run: |
           sudo pip install -r requirements/pip.txt
           sudo pip install -r requirements/edx/testing.txt
-          sudo pip install "django~=${{ matrix.django-version }}.0"
+          if [[ "${{ matrix.django-version }}" == "pinned" ]]; then
+            sudo pip install -r requirements/edx/django.txt
+          else
+            sudo pip install "django~=${{ matrix.django-version }}.0"
+          fi
+
+      - name: list installed package versions
+        run: |
+          sudo pip freeze
 
       - name: Setup and run tests
         uses: ./.github/actions/unit-tests
@@ -90,5 +102,3 @@ jobs:
           name: pytest-warning-report-html
           path: |
             reports/pytest_warnings/warning_report_all.html
-
-