fix: use 2.6.6 for milvus DDL upgrading

[chyezh]

issue: #43897

[sre-ci-robot]

[ci-v2-notice] Notice: We are gradually rolling out the new ci-v2 system.

• Legacy CI jobs remain unaffected, you can just ignore ci-v2 if you don't want to run it.
• Additional "ci-v2/*" checkers will run for this PR to ensure the new ci-v2 system is working as expected.
• For tests that exist in both v1 and v2, passing in either system is considered PASS.

To rerun ci-v2 checks, comment with:

• /ci-rerun-code-check // for ci-v2/code-check
• /ci-rerun-build // for ci-v2/build
• /ci-rerun-ut-integration // for ci-v2/ut-integration
• /ci-rerun-ut-go // for ci-v2/ut-go
• /ci-rerun-ut-cpp // for ci-v2/ut-cpp
• /ci-rerun-ut // for all ci-v2/ut-integration, ci-v2/ut-go, ci-v2/ut-cpp
• /ci-rerun-e2e-arm // for ci-v2/e2e-arm

If you have any questions or requests, please contact @zhikunyao.

[mergify[bot]]

@chyezh cpu-e2e job failed, comment /run-cpu-e2e can trigger the job again.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 76.49%. Comparing base (aa0870d) to head (9e79168). :warning: Report is 11 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #45738       +/-   ##
===========================================
- Coverage   83.19%   76.49%    -6.70%     
===========================================
  Files         521     1875     +1354     
  Lines       81430   292659   +211229     
===========================================
+ Hits        67744   223883   +156139     
- Misses      13686    61327    +47641     
- Partials        0     7449     +7449     

Components	Coverage Δ
Client	78.17% <ø> (∅)
Core	83.19% <ø> (ø)
Go	74.61% <75.36%> (∅)

Files with missing lines	Coverage Δ
...al/streamingcoord/server/balancer/balancer_impl.go	73.88% <ø> (ø)

... and 1353 files with indirect coverage changes

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• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[mergify[bot]]

@chyezh go-sdk check failed, comment rerun go-sdk can trigger the job again.

[chyezh]

rerun go-sdk

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chyezh, czs007

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• ~~OWNERS~~ [czs007]

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