bugfix: fix namingserver changVgroup failed

[ggbocoder]

• I have registered the PR changes.

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 52.52%. Comparing base (242d92c) to head (4930826).
Report is 4 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...ache/seata/namingserver/manager/NamingManager.java	50.00%	2 Missing and 3 partials ⚠️
...ache/seata/namingserver/entity/bo/NamespaceBO.java	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #6817      +/-   ##
============================================
+ Coverage     52.30%   52.52%   +0.22%     
+ Complexity     6387     6385       -2     
============================================
  Files          1080     1080              
  Lines         37552    37558       +6     
  Branches       4447     4450       +3     
============================================
+ Hits          19641    19729      +88     
+ Misses        15977    15881      -96     
- Partials       1934     1948      +14     

Files with missing lines	Coverage Δ
...ata/server/controller/VGroupMappingController.java	16.00% <ø> (+1.18%)	⬆️
...ache/seata/namingserver/entity/bo/NamespaceBO.java	59.09% <50.00%> (-14.60%)	⬇️
...ache/seata/namingserver/manager/NamingManager.java	55.50% <50.00%> (-1.24%)	⬇️

... and 17 files with indirect coverage changes

[funky-eyes]

LGTM