Bug 1895157 - Set always-target for buildconfig tasks r=jcristau

The buildconfig tasks are lint-like tasks that should run on-push whenever certain files are modified, even on try when not explicitly requested. The existing skip-unless-changed optimizations look correct, but always-target was missing.

Differential Revision: https://phabricator.services.mozilla.com/D209606

taskcluster/kinds/source-test/buildconfig.yml

@@ -4,6 +4,7 @@
 ---
 job-defaults:
     description: Make sure the content of .buildconfig.yml matches what gradle knows about its projects
+    always-target: true
     run:
         using: run-task
         cwd: '{checkout}'