Replace instanceof with Matchers#instanceOf in test cases

[mxsm]

• [x] I have searched the 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

[AlbumenJ]

Would you pls submit a PR to enhance?

[mxsm]

@AlbumenJ I will submit a pr to do this later

[elroykanye]

hi @AlbumenJ @mxsm still working on this? I'd like to work on it

[mxsm]

hi @AlbumenJ @mxsm still working on this? I'd like to work on it

I'm working on this.