[frontend] remove column 'source' from task errors (#5885)

[labo-flg]

source is not not queried, not in schema, so always empty

Proposed changes

• do not show the source column, until we have a proper solution to provide it

Related issues

• closes Background tasks errors never have a source info #5885

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (57e3a4b) 65.46% compared to head (707aacb) 66.02%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5987      +/-   ##
==========================================
+ Coverage   65.46%   66.02%   +0.56%     
==========================================
  Files         539      539              
  Lines       63094    63252     +158     
  Branches     5050     5454     +404     
==========================================
+ Hits        41302    41765     +463     
+ Misses      21792    21487     -305     

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