test: cover MockKestraApiServer namespace endpoint

[plisha39-dotcom]

What changes are being made and why?

Related to #5.

MockKestraApiServer lacks direct test coverage in this repository. This draft starts adding that coverage with a test for GET /api/v1/{tenantId}/namespaces/{id}.

The test starts the server, sends an HTTP request, and checks the status, Content-Type, and returned namespace ID. The HTTP client and server are closed after each test.

Remaining work:

• Validation endpoint
• Flow retrieval, including forced statuses
• Flow import and deletion
• ZIP export and filtering

How the changes have been QAed?

Ran ./gradlew test locally with Java 25: 63 tests passed, 0 failures, 0 skipped.

Contributor Checklist ✅

• I have read and followed the [plugin contribution guidelines](https://kestra.io/docs/plugin-developer-guide/contribution-guidelines)

[jymaire]

Thanks for PR, two small changes before PR approval

[jymaire]

Thanks for handling feedback so quickly 🚀

[jymaire]

Thanks for handling feedback so quickly 🚀

[Malaydewangan09]

@plisha39-dotcom, Just a small note for the future, if you could use GitHub Keywords when opening PRs to connect it to the proper issue (to automate the entire process a bit more), it would be super helpful to us. You can read a bit more about it here (I've added closing keyword for this particular issue)

[plisha39-dotcom]

Thanks for the review and guidance! This was my first open-source contribution, and I learned a lot along the way. I'll make sure to use closing keywords in future PRs that resolve an issue. Happy to have contributed!