Fix: Inversion in tagged mail searching

[stumpylog]

Proposed change

We want emails without the keyword, not those with the keyword.

Fixes #3302

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other (please explain)

Checklist:

• I have read & agree with the contributing guidelines.
• 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

Merging #3305 (552b029) into dev (fd84fc9) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev    #3305   +/-   ##
=======================================
  Coverage   93.35%   93.35%           
=======================================
  Files         156      156           
  Lines        6664     6664           
=======================================
  Hits         6221     6221           
  Misses        443      443           

Flag	Coverage Δ
backend	93.35% <100.00%> (ø)

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Impacted Files	Coverage Δ
src/paperless_mail/mail.py	88.23% <100.00%> (ø)

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[github-actions]

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