registry-cache-unit-tests: Use make verify-extended and reduce resouces

[ialidzhikov]

/kind enhancement

What this PR does / why we need it:
This PR adapts the registry-cache-unit-tests jobs in a way inspired by shoot-oidc-service jobs: https://github.com/gardener/ci-infra/blob/7a666e61f199138480e8dc2c5f28072801f27016/config/jobs/extension-shoot-oidc-service/extension-shoot-oidc-service-unit-tests.yaml

Which issue(s) this PR fixes:
Part of gardener/gardener-extension-registry-cache#3

Special notes for your reviewer:
N/A

[oliver-goetz]

/lgtm
/approve

[gardener-prow]

LGTM label has been added.

Git tree hash: b48e3e1d9943f1ba9d773513cffc95a5c9eb0237

[gardener-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: oliver-goetz

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [oliver-goetz]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[gardener-prow]

@ialidzhikov: Updated the job-config configmap in namespace prow at cluster gardener-prow-trusted using the following files:

• key gardener-extension-registry-cache-unit-tests.yaml using file config/jobs/gardener-extension-registry-cache/gardener-extension-registry-cache-unit-tests.yaml

In response to this:

/kind enhancement

What this PR does / why we need it:
This PR adapts the registry-cache-unit-tests jobs in a way inspired by shoot-oidc-service jobs: https://github.com/gardener/ci-infra/blob/7a666e61f199138480e8dc2c5f28072801f27016/config/jobs/extension-shoot-oidc-service/extension-shoot-oidc-service-unit-tests.yaml

Which issue(s) this PR fixes:
N/A

Special notes for your reviewer:
N/A

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.