matrix-tuwunel: pin version to v1.6.1

Repo convention is to pin homeserver-role versions to a specific tag
so renovate can track updates and so the deployment is reproducible.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/5200.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

roles/custom/matrix-tuwunel/defaults/main.yml

@@ -13,7 +13,7 @@ matrix_tuwunel_enabled: true
 matrix_tuwunel_hostname: ''
 
 # renovate: datasource=docker depName=ghcr.io/matrix-construct/tuwunel
-matrix_tuwunel_version: latest
+matrix_tuwunel_version: v1.6.1
 
 matrix_tuwunel_container_image: "{{ matrix_tuwunel_container_image_registry_prefix }}matrix-construct/tuwunel:{{ matrix_tuwunel_container_image_tag }}"
 matrix_tuwunel_container_image_tag: "{{ matrix_tuwunel_version }}"