Fix warnings from clippy 1.77

[Philippe-Cholet]

I triggered CI to see it fail: https://github.com/rust-itertools/itertools/actions/runs/8389675477/job/22976363676
Then I fixed the warnings (denied by CI).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.35%. Comparing base (6814180) to head (9d297fe).
Report is 41 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #908      +/-   ##
==========================================
- Coverage   94.38%   94.35%   -0.03%     
==========================================
  Files          48       48              
  Lines        6665     6807     +142     
==========================================
+ Hits         6291     6423     +132     
- Misses        374      384      +10     

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[phimuemue]

Thanks.