bump marvin image version to 0.2.3

[matheusfm]

Description

This PR bumps Marvin image version from 0.2.1 to 0.2.3.
I had only updated the version in go.mod and forgot to update the image in the last PR.

Linked Issues

UD-1367

How has this been tested?

• Creating a custom check which uses variables. Ex:

apiVersion: zora.undistro.io/v1alpha2
kind: CustomCheck
metadata:
  name: custom-002
spec:
  message: "Required labels"
  severity: Low
  category: Custom
  match:
    resources:
      - group: ""
        version: v1
        resource: pods
  params:
    requiredLabels:
      - app
  variables:
    - expression: "'exempt' in object.metadata.labels && object.metadata.labels['exempt'] == 'true'"
      name: exempt
  validations:
    - expression: >
        variables.exempt ||
        !object.metadata.labels.all(label, 
          params.requiredLabels.all(
            req, req != label
          )
        )
      message: "Pod without required labels"

Checklist

• I have labeled this PR with the relevant Type labels
• I have documented my code (if applicable)
• My changes are covered by tests

[lucasjct]

@matheusfm, lgtm