Extend tests for backup with multi vectorset case

[lferran]

Description

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How was this PR tested?

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.62%. Comparing base (a8a495f) to head (5d226f4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3112      +/-   ##
==========================================
+ Coverage   84.58%   84.62%   +0.03%     
==========================================
  Files         510      510              
  Lines       37735    37738       +3     
  Branches    11562    11562              
==========================================
+ Hits        31920    31937      +17     
+ Misses       5267     5252      -15     
- Partials      548      549       +1     

Flag	Coverage Δ
nidx	77.85% <ø> (-0.02%)	⬇️
nucliadb	78.49% <100.00%> (+0.10%)	⬆️
nucliadb-ingest	42.06% <0.00%> (-0.01%)	⬇️
nucliadb-reader	42.42% <0.00%> (-0.01%)	⬇️
nucliadb-search	45.87% <0.00%> (-0.01%)	⬇️
nucliadb-standalone	46.49% <25.00%> (-0.01%)	⬇️
nucliadb-train	45.02% <0.00%> (-0.01%)	⬇️
nucliadb-writer	46.86% <25.00%> (-0.01%)	⬇️
nucliadb_dataset	56.47% <ø> (ø)
nucliadb_models	83.54% <ø> (ø)
nucliadb_telemetry	85.10% <ø> (ø)
nucliadb_utils	84.97% <ø> (ø)

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