tikv: fix pessimistic txn not write binlog in master

[lysu]

What problem does this PR solve?

Problem Summary:

tk.MustExec("create table t(a int, b int)")
tk.MustExec("begin pessimistic")
tk.MustExec("insert into t select 1, 1")
tk.MustExec("commit")

shouldn't write 1, 1 binlog to downstream

What is changed and how it works?

What's Changed, How it Works:

#23873 will make BinlogExecutor lazy int until txn commit phase, but in pessimistic txn, twoPhaseCommitter can be created by DML lock operation before commit phase.

so SetBinlogExecutor set txn.2pc.binlog when txn.2pc != nil can fix this.

Related changes

• n/a

Check List

Tests

• Unit test

Side effects

• n/a

Release note

• n/a

---

This change is 

[lysu]

/rebuild

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• disksing
• youjiali1995

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[youjiali1995]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 523b785

[ti-chi-bot]

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