test(i): Handle error in test setup, don't return nil

[shahzadlone]

Relevant issue(s)

Resolves #3402

Description

In light of this PR:
https://github.com/sourcenetwork/defradb/pull/3400/files

I did a rip grep search:

 rg -U "if err != nil \{\n.*return nil$"

And found one more instance in the code base where non-nill error would still returning nil.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.20%. Comparing base (486f9da) to head (fca1262).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3403      +/-   ##
===========================================
- Coverage    78.24%   78.20%   -0.04%     
===========================================
  Files          392      392              
  Lines        36045    36045              
===========================================
- Hits         28202    28188      -14     
- Misses        6175     6184       +9     
- Partials      1668     1673       +5     

Flag	Coverage Δ
all-tests	78.20% <ø> (-0.04%)	⬇️

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see 12 files with indirect coverage changes

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[AndrewSisley]

LGTM, thanks for checking this Shahzad :)