[Buildkite] Move commtest retry setting to upper level

Summary: Addresses feedback from @bartek here: https://phab.comm.dev/D9569#281006

Test Plan: NA

Reviewers: bartek, ashoat, ginsu, tomek

Reviewed By: bartek

Subscribers: wyilio, bartek

Differential Revision: https://phab.comm.dev/D9614

.buildkite/commtest.yml

@@ -1,11 +1,11 @@
 steps:
   - label: ':docker: Run Commtest'
+    retry:
+      automatic: true
     plugins:
       - docker-compose#v4.14.0:
           run: commtest
           command: ['bash', 'run-tests-ci.sh']
-          retry:
-            automatic: true
           config:
             - services/docker-compose.yml
             - services/docker-compose.tests.yml