optimize: increase seata-core module unit test coverage

[lightClouds917]

• I have registered the PR changes.

Ⅰ. Describe what this PR did

optimize: increase seata-core module unit test coverage

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-commenter]

Codecov Report

Attention: 24 lines in your changes are missing coverage. Please review.

Comparison is base (01e6f0c) 49.86% compared to head (95d54bf) 50.38%.
Report is 2 commits behind head on 2.x.

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #6250      +/-   ##
============================================
+ Coverage     49.86%   50.38%   +0.52%     
- Complexity     4932     5035     +103     
============================================
  Files           917      917              
  Lines         31996    32010      +14     
  Branches       3862     3862              
============================================
+ Hits          15954    16129     +175     
+ Misses        14482    14315     -167     
- Partials       1560     1566       +6     

Files	Coverage Δ
.../io/seata/core/rpc/netty/v1/ProtocolV1Encoder.java	5.12% <ø> (ø)
.../rm/datasource/exec/BaseTransactionalExecutor.java	74.00% <100.00%> (+0.26%)	⬆️
.../seata/rm/datasource/exec/MultiUpdateExecutor.java	80.26% <100.00%> (+0.26%)	⬆️
...va/io/seata/rm/datasource/exec/UpdateExecutor.java	84.09% <100.00%> (+0.36%)	⬆️
...datasource/exec/mysql/MySQLUpdateJoinExecutor.java	78.48% <100.00%> (+0.13%)	⬆️
.../java/io/seata/sqlparser/druid/BaseRecognizer.java	80.95% <ø> (ø)
...a/sqlparser/druid/oracle/BaseOracleRecognizer.java	35.29% <ø> (ø)
...ser/druid/postgresql/BasePostgresqlRecognizer.java	23.21% <ø> (ø)
...arser/druid/sqlserver/BaseSqlServerRecognizer.java	54.54% <ø> (ø)
...ec/mysql/MySQLInsertOnDuplicateUpdateExecutor.java	32.16% <0.00%> (-0.17%)	⬇️
... and 3 more

... and 18 files with indirect coverage changes

[slievrly]

LGTM