Track backend/requirements.txt updates

.github/dependabot.yml

@@ -6,6 +6,12 @@ updates:
       interval: monthly
     target-branch: 'dev'
 
+  - package-ecosystem: pip
+    directory: '/backend'
+    schedule:
+      interval: monthly
+    target-branch: 'dev'
+
   - package-ecosystem: npm
     directory: '/'
     schedule: