Handle 404 error differently in InstitutionAttributeAggregator

[phavekes]

Addition to #144

[codecov]

Codecov Report

❌ Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.69%. Comparing base (4b0df56) to head (0f3891c).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...rs/institution/InstitutionAttributeAggregator.java	42.85%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #145      +/-   ##
============================================
- Coverage     95.17%   94.69%   -0.48%     
  Complexity      316      316              
============================================
  Files            55       55              
  Lines           994      999       +5     
  Branches         74       75       +1     
============================================
  Hits            946      946              
- Misses           21       25       +4     
- Partials         27       28       +1     

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