Variable substitution doesn't work in configmap/secret items from volume

[FogDong]

Expected Behavior

The variable in configmap/secret items will be substituted.

Actual Behavior

I set the variable substition in configmap items but it didn't work, and the pod created failed since the items key and path can not found.

Steps to Reproduce the Problem

1. Create a task with configmap volume.

Additional Info

• Kubernetes version:

  Output of kubectl version:

  Client Version: version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.5", GitCommit:"e6503f8d8f769ace2f338794c914a96fc335df0f", GitTreeState:"clean", BuildDate:"2020-07-04T15:01:15Z", GoVersion:"go1.14.4", Compiler:"gc", Platform:"darwin/amd64"}

• Tekton Pipeline version:

  Output of tkn version or kubectl get pods -n tekton-pipelines -l app=tekton-pipelines-controller -o=jsonpath='{.items[0].metadata.labels.version}' devel from master