build: the Django matrix needs to use the pinned version also.

The logic here seems to work, but Django 4.0 won't install over our
other pinned requirements, so tests fail for Django 4.0.

.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
-
-