pod group typo

Author: kannon92

keps/sig-scheduling/4671-gang-scheduling/README.md

@@ -153,7 +153,7 @@ spec:
     spec:
       workloadRef:
         name: job-1
-        podgroup: pg1
+        podGroup: pg1
       restartPolicy: OnFailure
       containers:
       - name: ml-worker