bugfix: fix the Raft NPE issue caused by two-phase concurrency

[funky-eyes]

• I have registered the PR changes.

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

fixes #7004

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 27.58621% with 21 lines in your changes missing coverage. Please review.

Project coverage is 52.60%. Comparing base (dbe095a) to head (652a7f2).
Report is 1 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...aft/execute/branch/UpdateBranchSessionExecute.java	28.57%	8 Missing and 2 partials ⚠️
...r/raft/execute/branch/AddBranchSessionExecute.java	28.57%	4 Missing and 1 partial ⚠️
...er/raft/execute/lock/BranchReleaseLockExecute.java	28.57%	4 Missing and 1 partial ⚠️
...e/seata/server/session/SessionStatusValidator.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #7005      +/-   ##
============================================
- Coverage     52.61%   52.60%   -0.02%     
- Complexity     6579     6580       +1     
============================================
  Files          1126     1126              
  Lines         39928    39953      +25     
  Branches       4680     4690      +10     
============================================
+ Hits          21010    21019       +9     
- Misses        16916    16930      +14     
- Partials       2002     2004       +2     

Files with missing lines	Coverage Δ
...e/seata/server/session/SessionStatusValidator.java	46.66% <0.00%> (-3.34%)	⬇️
...r/raft/execute/branch/AddBranchSessionExecute.java	55.55% <28.57%> (-19.45%)	⬇️
...er/raft/execute/lock/BranchReleaseLockExecute.java	40.00% <28.57%> (-15.56%)	⬇️
...aft/execute/branch/UpdateBranchSessionExecute.java	45.45% <28.57%> (-34.55%)	⬇️

... and 2 files with indirect coverage changes

[slievrly]

LGTM