test: add some UT cases for config module

[slievrly]

• I have registered the PR changes.

Ⅰ. Describe what this PR did

add some UT cases for config module

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 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 51.46%. Comparing base (01877a9) to head (cefa249).

Files with missing lines	Patch %	Lines
...pache/seata/config/apollo/ApolloConfiguration.java	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #7197      +/-   ##
============================================
- Coverage     51.49%   51.46%   -0.03%     
- Complexity     6819     6841      +22     
============================================
  Files          1169     1171       +2     
  Lines         41567    41720     +153     
  Branches       4872     4897      +25     
============================================
+ Hits          21405    21473      +68     
- Misses        18135    18212      +77     
- Partials       2027     2035       +8     

Files with missing lines	Coverage Δ
...pache/seata/config/consul/ConsulConfiguration.java	39.47% <ø> (ø)
...pache/seata/config/apollo/ApolloConfiguration.java	62.19% <66.66%> (+9.18%)	⬆️

... and 5 files with indirect coverage changes

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