Fix flaky file-based indexing tests

[varunbharadwaj]

Description

File-based indexing test, especially FileBasedIngestionSingleNodeTests.testFileIngestionFromLatestPointer has been marked flaky as it fails expecting 0 results, but returns 2.

This could happen if the file contents are not visible at the time of poller initialization. This PR updates the setup stage to ensure the file contents are visible.

However, this could not be reproduced locally even on running 500 iterations. We'll monitor if the issue is solved after this change.

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[github-actions]

✅ Gradle check result for 2d03d63: SUCCESS

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.18%. Comparing base (8feb6e1) to head (2d03d63).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #19735      +/-   ##
============================================
+ Coverage     73.11%   73.18%   +0.06%     
- Complexity    70823    70882      +59     
============================================
  Files          5732     5732              
  Lines        324255   324255              
  Branches      46924    46924              
============================================
+ Hits         237087   237306     +219     
+ Misses        68076    67843     -233     
- Partials      19092    19106      +14     

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