Description of problem:

PipelineRuns using workspaces may fail in 1.15 due to the workspaces not being marked as optional. This seems like it is the intended behavior, but this does not occur in 1.14, which can lead to breaking user's pipelines on upgrade to 1.15.

No presently known workaround other than explicitly marking the workspace as optional.

Prerequisites (if any, like setup, operators/versions):

OpenShift Pipelines 1.15

Steps to Reproduce

1.  Install Pipelines 1.15 to OCP cluster
2. Create PipelineRun with (unneeded) workspace that's not marked optional:

---
apiVersion: tekton.dev/v1
kind: PipelineRun
metadata:
  name: test-workspace-plr
spec:
  pipelineSpec:
    tasks:
      - name: echo-hello
        taskSpec:
          steps:
            - name: echo
              image: registry.access.redhat.com/ubi9/ubi-micro
              env:
                - name: HOME
                  value: $(workspaces.source.path)  # note workspace mentioned here
              script: |
                #!/usr/bin/env bash
                echo "hello world"

Actual results:

PipelineRun will fail in 1.15, citing error

expected workspace "source" to be provided by pipelinerun for pipeline task "echo-hello"

PipelineRun runs just fine in 1.14.

Expected results:

PipelineRun fails in both 1.14 and 1.15, but more importantly, this change is documented if expected.

Reproducibility (Always/Intermittent/Only Once):

Always

Acceptance criteria: 

Issue is clarified to be unintentional, or is documented as a breaking change in 1.15