bugfix: fix ConcurrentModificationException in SessionConverter.convertBranchSession

[psxjoy]

• I have registered the PR changes.
• I have added test cases and all cases have passed.

Ⅰ. Describe what this PR did

• fix ConcurrentModificationException in SessionConverter.convertBranchSession(List<BranchSession> branchSessions).
• fix a typo in README.md.

Ⅱ. Does this pull request fix one issue?

fix #6895

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

I have added test cases and all cases have passed,not applicable.

已添加相关测试用例并且用例通过，不适用该选项。

Ⅳ. Describe how to verify it

Run SessionConverterTest

Ⅴ. Special notes for reviews

Since the issue cannot be consistently reproduced in a multithreaded environment, I configured the test cases to run 100 times. However, this method is too resource-intensive and time-consuming. I decided to comment out those test cases and will reevaluate their necessity later.

多线程问题无法100%复现，因此测试用例设置为重复运行100次。但是这样的测试用例太过于消耗运行资源和时间。我暂时将对应的测试用例注释掉，待评估后再正常使用。

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 52.69%. Comparing base (dbeba61) to head (b02dd7f).
Report is 1 commits behind head on 2.x.

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #6943      +/-   ##
============================================
+ Coverage     52.68%   52.69%   +0.01%     
- Complexity     6559     6560       +1     
============================================
  Files          1122     1122              
  Lines         39861    39862       +1     
  Branches       4666     4668       +2     
============================================
+ Hits          21001    21007       +6     
+ Misses        16862    16860       -2     
+ Partials       1998     1995       -3     

Files with missing lines	Coverage Δ
.../apache/seata/server/storage/SessionConverter.java	89.60% <100.00%> (+0.08%)	⬆️

... and 7 files with indirect coverage changes

[xingfudeshi]

LGTM