[CLA Required] Update variables.tf

[lilongthinker]

upgrade ack cluster version from 1.14.8-aliyun.1 to 1.18.8-aliyun.1

1.14.8-aliyun.1 is unsupported

What problem does this PR solve?

What is changed and how does it work?

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• DanielZhangQD
• KanShiori

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[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ DanielZhangQD
❌ lilongthinker
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[DanielZhangQD]

@lilongthinker Please sign the CLA, thanks!

[DanielZhangQD]

LGTM

[codecov-commenter]

Codecov Report

Merging #4162 (f8ba660) into master (e865837) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4162   +/-   ##
=======================================
  Coverage   61.28%   61.29%           
=======================================
  Files         178      178           
  Lines       18986    18986           
=======================================
+ Hits        11636    11637    +1     
+ Misses       6206     6205    -1     
  Partials     1144     1144           

Flag	Coverage Δ
unittest	61.29% <ø> (+<0.01%)	⬆️

[DanielZhangQD]

@lilongthinker Could you please sign the CLA? Thanks!