ci: enable Dependabot checks for Python

.github/dependabot.yml

@@ -9,3 +9,11 @@ updates:
     labels:
       - "type/build"
       - "scope/dockerfile"
+
+  # Maintain Python dependencies (test suite)
+  - package-ecosystem: "pip"
+    directory: "/test/requirements"
+    schedule:
+      interval: "daily"
+    labels:
+      - "type/ci"