lints: update to golangci-lint v2.6

[cyphar]

Signed-off-by: Aleksa Sarai cyphar@cyphar.com

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.04%. Comparing base (a058839) to head (4716af5).
⚠️ Report is 37 commits behind head on main.
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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #651      +/-   ##
==========================================
+ Coverage   72.89%   74.04%   +1.15%     
==========================================
  Files          71       71              
  Lines        6164     4635    -1529     
==========================================
- Hits         4493     3432    -1061     
+ Misses       1213      749     -464     
+ Partials      458      454       -4     

Files with missing lines	Coverage Δ
internal/system/xattr_unix.go	73.33% <100.00%> (+3.63%)	⬆️
oci/layer/tar_extract.go	53.43% <100.00%> (-3.62%)	⬇️
pkg/fseval/fseval_default.go	91.30% <100.00%> (+0.91%)	⬆️
pkg/fseval/fseval_rootless.go	95.74% <100.00%> (ø)

... and 57 files with indirect coverage changes

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