Update Mjolnir from v1.2.1 to v1.3.1

roles/matrix-bot-mjolnir/defaults/main.yml

@@ -3,7 +3,7 @@
 
 matrix_bot_mjolnir_enabled: true
 
-matrix_bot_mjolnir_version: "v1.2.1"
+matrix_bot_mjolnir_version: "v1.3.1"
 
 matrix_bot_mjolnir_container_image_self_build: false
 matrix_bot_mjolnir_container_image_self_build_repo: "https://github.com/matrix-org/mjolnir.git"