Fix CodeQL warnings about lack of workflow permissions

Author: timgraham

.github/workflows/test-python-atlas.yml

@@ -54,3 +54,5 @@ jobs:
         run: bash .github/workflows/start_local_atlas.sh mongodb/mongodb-atlas-local:7
       - name: Run tests
         run: python3 django_repo/tests/runtests.py --settings mongodb_settings -v 2
+    permissions:
+        contents: read

.github/workflows/test-python.yml

@@ -55,3 +55,5 @@ jobs:
           mongodb-version: 6.0
       - name: Run tests
         run: python3 django_repo/tests/runtests_.py
+    permissions:
+        contents: read