Updated regex pattern to allow all three valid bracket notations.

[chitrangpatel]

Changes

Updated regex pattern to allow all three valid bracket notations.

Prior to this, when supplied parameter name was not the same as that
called in the step, webhook raised an error when using the dot notation
as expected. However, it did not when using the bracket notation.

Updated the unit tests to also check for valid bracket notations.
This PR addresses issue #4787 and #4792

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Hi @chitrangpatel. Thanks for your PR.

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[chuangw6]

Adding this else will not work because different values can be passed to ValidateVariableP function other than just param names i.e. image name, step name.

apiVersion: tekton.dev/v1beta1
kind: TaskRun
metadata:
  generateName: validation-
spec:
  taskSpec:
    params:
      - name: foo
        default: "bar1"
    results:
      - name: echo-output
        description: "successful echo"
    steps:
      - name: echo-params
        image: bash
        script: |
          set -e
          echo $(params.foo) | tee $(results.echo-output.path)

Try this example, when you apply, you'll see

Error from server (BadRequest): error when creating "validation.yaml": admission webhook "validation.webhook.pipeline.tekton.dev" denied the request: validation failed: Expected to find variables but none found in "": spec.taskSpec.steps[0].workingDir
Expected to find variables but none found in "bash": spec.taskSpec.steps[0].image
Expected to find variables but none found in "echo-params": spec.taskSpec.steps[0].name
Expected to find variables but none found in "set -e\necho $(params.foo) | tee $(results.echo-output.path)\n": spec.taskSpec.steps[0].script