uucore: fix clippy warnings

[bakanovskii]

Fixes: #8653

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[codspeed-hq]

CodSpeed Performance Report

Merging #8769 will not alter performance

_{Comparing bakanovskii:uucore-fix-clippy (089faa5) with main (5c15d79)}

Summary

✅ 41 untouched
⏩ 64 skipped¹

Footnotes

1. 64 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[cakebaker]

Thanks!