fix: avoid unused_variables under Windows

[waynexia]

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Refer to a related PR or issue link (optional)

Fixes https://github.com/GreptimeTeam/greptimedb/actions/runs/8808344307

What's changed and what's your intention?

Checklist

• [ ] I have written the necessary rustdoc comments.
• [ ] I have added the necessary unit tests and integration tests.
• [x] This PR does not require documentation updates.

[waynexia]

Test pipeline against this branch: https://github.com/GreptimeTeam/greptimedb/actions/runs/8810252748

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 85.57%. Comparing base (f764fd5) to head (acd4b25). Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3786      +/-   ##
==========================================
+ Coverage   85.52%   85.57%   +0.04%     
==========================================
  Files         946      946              
  Lines      159621   159929     +308     
==========================================
+ Hits       136511   136852     +341     
+ Misses      23110    23077      -33     

[tisonkun]

@waynexia can we move forward this draft? I don't see anything pending here :O