ci: update decision docker image (#698)

* ci: update decision docker image

* ci: move decision task from AWS to GCP

.taskcluster.yml

@@ -155,7 +155,7 @@ tasks:
                                         name: "Decision Task for cron job ${cron.job_name}"
                                         description: 'Created by a [cron task](https://tools.taskcluster.net/tasks/${cron.task_id})'
                       provisionerId: "xpi-${level}"
-                      workerType: "decision"
+                      workerType: "decision-gcp"
                       tags:
                           $if: 'tasks_for in ["github-push", "github-pull-request"]'
                           then:
@@ -243,7 +243,7 @@ tasks:
                               chainOfTrust: true
                           # Note: This task is built server side without the context or tooling that
                           # exist in tree so we must hard code the hash
-                          image: mozillareleases/taskgraph:decision-cf4b4b4baff57d84c1f9ec8fcd70c9839b70a7d66e6430a6c41ffe67252faa19@sha256:425e07f6813804483bc5a7258288a7684d182617ceeaa0176901ccc7702dfe28
+                          image: mozillareleases/taskgraph:decision-5483484ad45a3d27a0f5bd05f1c87d90e08df67a3713605d812b851a8a5bd854@sha256:ef132cc5741539f846a85bbe0cebc3c9ead30b8f24c1da46c55363f2170c3993
 
                           maxRunTime: 1800