Fix: only count inbox documents from inbox tags with permissions

[shamoon]

Proposed change

Slightly specific set of circumstances but surprised this hasn't come up already. The test here fails without the change.

Closes #6654

Type of change

• Bug fix: non-breaking change which fixes an issue.
• New feature / Enhancement: non-breaking change which adds functionality. Please read the important note above.
• Breaking change: fix or feature that would cause existing functionality to not work as expected.
• Documentation only.
• Other. Please explain:

Checklist:

• I have read & agree with the contributing guidelines.
• If applicable, I have included testing coverage for new code in this PR, for backend and / or front-end changes.
• If applicable, I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• If applicable, I have checked that all tests pass, see documentation.
• I have run all pre-commit hooks, see documentation.
• I have made corresponding changes to the documentation as needed.
• I have checked my modifications for any breaking changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.19%. Comparing base (74b8504) to head (2167fbd).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #6670   +/-   ##
=======================================
  Coverage   97.19%   97.19%           
=======================================
  Files         436      436           
  Lines       17968    17968           
  Branches     1523     1431   -92     
=======================================
  Hits        17464    17464           
- Misses        501      504    +3     
+ Partials        3        0    -3     

Flag	Coverage Δ
backend	95.88% <ø> (ø)
frontend	98.63% <ø> (ø)

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[stumpylog]

Thanks for the diligence in tracking it down