Replace instanceof with Matchers#instanceOf in test cases

- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 3.2
* Operating System version: ALL
* Java version: xxx

### Steps to reproduce this issue

In some test cases use instanceof, for example ExtensionTest class
we can replace with Matchers#instanceOf

### Expected Behavior

```
MatcherAssert.assertThat(myfactory, Matchers.instanceOf(ExtensionInjector.class));
```

### Actual Behavior

Start with the ExtensionTest class mentioned in the issue and search the test sources for instanceof assertions. Run the affected tests, and consider the work complete when the relevant test cases use Matchers.instanceOf consistently and still pass.

Written by the indexing model from the issue text.