Bug 1691479 - demote Bugzilla task to tier 2 because it only runs on mozilla-central. r=jmaher DONTBUILD

The 'Bugzilla' task which e.g. creates the mapping of files to Bugzilla
components only runs on mozilla-central since bug 1608421. This means its
failures don't justify a backout and the task should be tier 2 for which
developers get needinfoed and fix the issue in a follow-up. If there is no
action, the changes can still be backed out.

Differential Revision: https://phabricator.services.mozilla.com/D104425

taskcluster/ci/source-test/file-metadata.yml

@@ -22,6 +22,7 @@ bugzilla-components:
     description: Generate metadata about source files and Bugzilla
     treeherder:
         symbol: Bugzilla
+        tier: 2
     index:
         product: source
         job-name: source-bugzilla-info