[Unit Test] Update Unit tests for eventmesh-runtime admin endpoints

### Search before asking

- [X] I had searched in the [issues](https://github.com/apache/eventmesh/issues?q=is%3Aissue) and found no similar issues.

### Read the unit testing guidelines

- [X] I have read.

### Unit test request

As a result of the refactoring of https://github.com/apache/eventmesh/pull/4768, all of the unit test classes no longer work and need to be rewritten using Netty.

### Describe the unit tests you want to do

Module name: eventmesh-runtime
Located at: org.apache.eventmesh.runtime.admin.handler
Task status: ×(unfinished)

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!