sink: fix concurrent map access in sink manager (#2249)

[ti-chi-bot]

This is an automated cherry-pick of #2249

What problem does this PR solve?

• There is an unsynchronized access to a shared map, which can cause runtime panic.

What is changed and how it works?

• Lock it.

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

• Fix minor runtime panic risk

[ti-chi-bot]

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[amyangfei]

/merge

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (release-5.0@e94f5f5). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff                @@
##             release-5.0      #2299   +/-   ##
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  Files                  ?        166           
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  Hits                   ?      10877           
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  Partials               ?       1047           

[amyangfei]

/merge

[amyangfei]

/merge

[amyangfei]

/merge

[ti-chi-bot]

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

Commit hash: 38f1bb8

[amyangfei]

/run-leak-tests

[amyangfei]

/run-leak-tests
/run-kafka-tests