lib: warn for clippy::use_self

[cpu]

This was accidentally added to the allow lints instead of the warn lints in #262.

[djc]

You added it to deny instead of warn. 🤪

[codecov]

Codecov Report

Attention: Patch coverage is 45.28302% with 29 lines in your changes missing coverage. Please review.

Project coverage is 97.30%. Comparing base (c399cd9) to head (65d439c).

Files	Patch %	Lines
src/error.rs	21.62%	29 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #263   +/-   ##
=======================================
  Coverage   97.30%   97.30%           
=======================================
  Files          19       19           
  Lines        4237     4237           
=======================================
  Hits         4123     4123           
  Misses        114      114           

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[cpu]

You added it to deny instead of warn.

😆 muttering something about needing more coffee

Fixed