fix(e2e): fix openapi git url

[nilgaar]

Description

fixing e2e, as openapi example is moved into a new repo:
https://gcsweb-ci.apps.ci.l2s4.p1.openshiftapps.com/gcs/test-platform-results/logs/periodic-ci-janus-idp-backstage-showcase-release-1.3-e2e-tests-nightly/1853678691410776064/artifacts/e2e-tests-nightly/janus-idp-backstage-showcase-release-1.3-nightly/artifacts/showcase-ci-nightly/index.html#?testId=d49d675e7afa73fe2c07-0f496372062f0d27578a

reference:
OAI/OpenAPI-Specification#4172
https://redhat-internal.slack.com/archives/C07D05S8U82/p1730789892014959

Which issue(s) does this PR fix

no ticket open

PR acceptance criteria

Please make sure that the following steps are complete:

• GitHub Actions are completed and successful
• Unit Tests are updated and passing
• E2E Tests are updated and passing
• Documentation is updated if necessary (requirement for new features)
• Add a screenshot if the change is UX/UI related

How to test changes / Special notes to the reviewer

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[github-actions]

The image is available at: quay.io/janus-idp/backstage-showcase:pr-1878!