0.15.0: "TaskRun mounts more than one PersistentVolumeClaim" despite single PVC w/ workspace subDirs

[bitsofinfo]

I have a task theTask with 2 named workspaces:

...
  workspaces:

    - name: app-source
      description: The workspace where the app source code resides
      mountPath: /workspace/app-source
      readOnly: false

    - name: secondary-source
      description: The workspace where the secondary source code resides
      mountPath: /workspace/secondary-source
      readOnly: false
...

I have a pipeline with 1 workspace that is mapped to the 2 task workspaces via the diffentiating subPath flag:

    - name: theTask
      taskRef:
        name: theTask

      runAfter: 
        - init

      workspaces:
        - name: secondary-source
          workspace: build-ops
          subPath: secondary-source
        - name: app-source
          workspace: build-ops
          subPath: app-source
    

This worked totally fine up to 0.14.3 but now fails with this error in 0.15.0 and broke several functioning pipelines

 TaskRun mounts more than one PersistentVolumeClaim - that is forbidden
      when the Affinity Assistant is enabled

Related I assume: #2885

Seems one should still be above to mount a single PVC, which is what this is, its just logically divided by the different subPaths, vs truly separate PVCs which I am not attempting to do.

[vdemeester]

/cc @jlpettersson