feat: increase coverage

[matmair]

Increase coverage of the backend and fix various small things discovered during test writing; Preparation for #8874

[netlify]

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Name	Link
🔨 Latest commit	8b59561
🔍 Latest deploy log	https://app.netlify.com/sites/inventree-web-pui-preview/deploys/678ed194ab82d60008180b31

[codecov]

Codecov Report

Attention: Patch coverage is 97.82609% with 6 lines in your changes missing coverage. Please review.

Project coverage is 85.39%. Comparing base (f602c43) to head (8b59561).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...rc/backend/InvenTree/report/templatetags/report.py	88.00%	3 Missing ⚠️
src/backend/InvenTree/report/tests.py	71.42%	2 Missing ⚠️
src/backend/InvenTree/report/test_tags.py	99.54%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8897      +/-   ##
==========================================
+ Coverage   85.17%   85.39%   +0.22%     
==========================================
  Files        1175     1179       +4     
  Lines       51808    51881      +73     
  Branches     2106     2099       -7     
==========================================
+ Hits        44127    44304     +177     
+ Misses       7147     7042     -105     
- Partials      534      535       +1     

Flag	Coverage Δ
backend	87.21% <97.82%> (+0.25%)	⬆️

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[SchrodingersGat]

@matmair please address conflicts here and then I'm happy to merge :)

[matmair]

@SchrodingersGat done