[ci]: Fix official build not existing issue (sonic-net#7408)

When submitting a new official build for broadcom, vs, it prompts a error message, which says the job is not defined.
It was caused by the default option "[]", which is not empty, it is used as the jobGroups parameter.

.azure-pipelines/azure-pipelines-build.yml

@@ -15,7 +15,7 @@ parameters:
   default: []
 - name: 'jobGroups'
   type: object
-  default: []
+  default: ''
 
 jobs:
 - template: azure-pipelines-image-template.yml