br: security update br image:1.18.1-alpine to 1.18.9-alpine (#40863)

[ti-chi-bot]

This is an automated cherry-pick of #40863

What problem does this PR solve?

Issue Number: ref #39052

Problem Summary:

There are serveral critical vulnerabilities detected in this repository, which located in br/docker/Dockerfile. Now we recommand upgrading the base image of this dockerfile to avoid vulnerabilities.

What is changed and how it works?

Changed the base image of br:

• br/docker/Dockerfile
• We recommend upgrading to golang:1.18.9-alpine, as this image has only 0 known vulnerabilities. To do this, merge this pull request, then verify your application still works as expected.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Just upgrade the base image of BR tool, to fix known vulnerabilities. 
If possible, you can upgrade the base image under the br directory of all branches to this version.

/cc @xhebox ,PTAL

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• 3pointer
• joccau

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[joccau]

LGTM

[joccau]

/merge

[ti-chi-bot]

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

Commit hash: 7175d87