[Dubbo]: Fix the bug that isDefault configuration is not useful #12961

[paradiseidler]

What is the purpose of the change?

Fix #12961 The tag with attribute=false for the isDefault property has been removed.

In the isIgnoredAttribute method, due to isDefault having attribute=false, the entire method returns a Boolean value of true.

In the assignProperties method of the AbstractConfig class, at the breakpoint, the final condition evaluates to false, preventing the default property assignment process from being executed, resulting in the default value remaining unprocessed as null.

Checklist

• [x] Make sure there is a GitHub_issue field for the change.
• [x] Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• [x] Write necessary unit-test to verify your logic correction. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• [x] Make sure gitHub actions can pass. Why the workflow is failing and how to fix it?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 2.20%. Comparing base (ef6e8bd) to head (69de5fb). Report is 56 commits behind head on 3.3.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## 3.3 #14888 +/- ## ============================================= - Coverage 37.53% 2.20% -35.34% ============================================= Files 1813 26083 +24270 Lines 80737 1389674 +1308937 Branches 12005 220210 +208205 ============================================= + Hits 30304 30588 +284 - Misses 46042 1354645 +1308603 - Partials 4391 4441 +50 ```

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