Tekton pipeline not showing diff after upgrade

Question

We recently upgraded our Kubernetes cluster and due to that, we had to upgrade Tekton and Prow. After the upgrade, we had to make changes to the Prow job's pre and postsubmit config and we had to change PROW_IMPLICIT_GIT_REF to git which is a PipelineResource.

Now the issue is, with the earlier version due to PROW_IMPLICIT_GIT_REF we could see a diff of the changes that we are pushing to the Environment. Now there is no way to get a diff of the changes we are pushing. We tried creating our own param and passing it from the Prow job to PipelineResource but that also is not working as it is not getting the value for the git branch. Below is the pipeline resource we are using and the Prow job config is also given below. We tried various params like params.branch or directly passing PULL_BASE_REF to the PipelineResource but nothing worked.

Can anyone help me with how we can pass the git branch info from prow job to tekton pipelineresource and this way we can pass the correct branch name to the helm diff command and get the diff of the changes we are pushing.

Prow-job:

presubmits:
  Org/env-state:
    - name: job-name
      namespace: tekton-pipelines
      agent: tekton-pipeline
      max_concurrency: 1
      clone_uri: <git-url>
      run_if_changed: "^folder/somefiles.yaml"
      branches:
        - ^master$
      pipeline_run_spec:
        pipelineRef:
          name: upgrade-env-pipeline
        params:
          - name: cluster-name
            value: test
          - name: DRY_RUN
            value: "true"
          - name: CMD_IMAGE
            value: pipeline-infra
          - name: CMD_BRANCH
            value: master
          - name: BRANCH_NAME
            value: $(PULL_BASE_REF)
        resources:
          - name: git
            resourceRef:
              name: git

PipelineResource:

apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: git
  namespace: tekton-pipelines
spec:
  params:
  - name: revision
    value: $(params.BRANCH_NAME)
  - name: url
    value: <git-url>
  type: git