[CON-151] fix: test: replace flaky Sleep with more predictable wait

[arajasek]

As in the title, this should prevent this test from flaking (or at least decrease the likelihood).

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Dec 22, 2025, 9:26 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 42.00%. Comparing base (cfa7ea6) to head (ecc7519).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2642      +/-   ##
==========================================
- Coverage   43.71%   42.00%   -1.72%     
==========================================
  Files        1902     1018     -884     
  Lines      158677    84807   -73870     
==========================================
- Hits        69373    35624   -33749     
+ Misses      82914    45841   -37073     
+ Partials     6390     3342    -3048     

Flag	Coverage Δ
sei-chain	?
sei-cosmos	38.20% <ø> (ø)
sei-db	69.06% <ø> (ø)
sei-tendermint	47.32% <ø> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.
see 895 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.