Modify min k8s version to v.1.28.0 as supported by minikube action

[devanshuVmware]

• Bump git ref for bitnami/nginx example test

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?

Additional Notes for your reviewer:

Review Checklist:

• [ ] Follows the developer guidelines
• [ ] Relevant tests are added or updated
• [ ] Relevant docs in this repo added or updated
• [ ] Relevant carvel.dev docs added or updated in a separate PR and there's a link to that PR
• [ ] Code is at least as readable and maintainable as it was before this change

Additional documentation e.g., Proposal, usage docs, etc.: