Bump default auto-deploy-image to 2.18.1

This version includes a bug fix for the agent to work with the Auto
Deploy feature of Auto DevOps. See related issue:

https://gitlab.com/gitlab-org/cluster-integration/auto-deploy-image/-/issues/191

Changelog: fixed

lib/gitlab/ci/templates/Jobs/Deploy.gitlab-ci.yml

 variables:
-  AUTO_DEPLOY_IMAGE_VERSION: 'v2.17.0'
+  AUTO_DEPLOY_IMAGE_VERSION: 'v2.18.1'
 
 .auto-deploy:
   image: "registry.gitlab.com/gitlab-org/cluster-integration/auto-deploy-image:${AUTO_DEPLOY_IMAGE_VERSION}"