Don't run tasks for mergify branches on push (#17489)

.taskcluster.yml

@@ -103,7 +103,7 @@ tasks:
               $if: >
                 tasks_for in ["action", "cron"]
                 || (tasks_for == "github-pull-request" && pullRequestAction in ["opened", "reopened", "synchronize"])
-                || (tasks_for == "github-push" && head_branch[:10] != "refs/tags/") && (head_branch != "staging.tmp") && (head_branch != "trying.tmp")
+                || (tasks_for == "github-push" && head_branch[:10] != "refs/tags/") && (head_branch != "staging.tmp") && (head_branch != "trying.tmp") && (head_branch[:8] != "mergify/")
                 || (tasks_for == "github-release" && releaseAction == "published" && (ownerEmail != "mozilla-release-automation-bot@users.noreply.github.com") && (ownerEmail != "mozilla-release-automation-bot-staging@users.noreply.github.com"))
               then:
                   $let: