Description of problem:

  In OpenShift Pipelines 1.9 release the marshalJSON function cannot marshal lists. 

Prerequisites:
OpenShift 4.12.0
Openshift-pipelines operator : 1.9 

Steps to Reproduce:

1. Send JSON payload (from Knative in this case) to the EventListener pod
2. use 'marshalJSON()' inside TriggerTemplate to process this JSON payload
3. View logs inside the EventListener pod

Actual results:
The actual behavior is that the Pipeline doesn't even start at all. The EventListener pod gives the following error.

rpc error: code = InvalidArgument desc = error evaluating cel expression: expression \"body.spec.tags.marshalJSO

Expected results:

The expected behavior is that the pipeline starts and the correct JSON information is geven as parameter to the Pipeline.
Knative sends JSON data to the EventListener pod and uses the marshalJSON function to make a string of it for the next Task.

Build Details:
Tekton Pipeline version:
Client version: 0.28.0
Pipeline version: v0.41.0
Triggers version: v0.22.0
Operator version: v0.63.0

Additional info (Such as Logs, Screenshots, etc):

Upstream Github issue: https://github.com/tektoncd/triggers/issues/1538