[BUGFIX] argilla-server: await on similarity search when filtering response values without user

[frascuchon]

Description

This PR fixes missing await call included in #5003

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested

Checklist

• I added relevant documentation
• follows the style guidelines of this project
• I did a self-review of my code
• I made corresponding changes to the documentation
• I confirm My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.96%. Comparing base (239d6b1) to head (9bdc5de).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5159      +/-   ##
===========================================
+ Coverage    91.94%   91.96%   +0.01%     
===========================================
  Files          135      135              
  Lines         5819     5821       +2     
===========================================
+ Hits          5350     5353       +3     
+ Misses         469      468       -1     

Flag	Coverage Δ
argilla-server	91.96% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.