Fix flaky tests

[Turbo87]

It looks like the pool.timeout_get() fn does not actually retry connecting until the timeout is elapsed and instead fails instantly. this PR changes the wait_until_healthy() fn to retry connecting in a loop until the timeout is elapsed. I ran the CI pipeline multiple times with this change and wasn't able to trigger the failing tests anymore, so hopefully this fixes the flaky tests.

[codecov]

Codecov Report

Attention: Patch coverage is 91.30435% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 87.64%. Comparing base (1af5ce3) to head (e8083ef).

❗ Current head e8083ef differs from pull request most recent head 6bb0b15. Consider uploading reports for the commit 6bb0b15 to get more accurate results

Files	Patch %	Lines
src/tests/unhealthy_database.rs	91.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8449      +/-   ##
==========================================
- Coverage   87.65%   87.64%   -0.01%     
==========================================
  Files         272      272              
  Lines       26193    26202       +9     
==========================================
+ Hits        22959    22966       +7     
- Misses       3234     3236       +2     

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