**Backport:** https://codeberg.org/forgejo/forgejo/pulls/2906
Following #2763 (refactor of git check-attr)
and #2866 (wrong log.Error format in check-attr)
- refactors the `nul-byte` reader to be used in both the streaming and one-off cases.
- add test for some failure cases
- don't log the error returned by `cmd.Run`, but return it to the `CheckPath` caller (which can then decide what to do with it).
This should solve the following flaky `log.Error` (or at least move it to the caller, instead of being inside a random goroutine):
https://codeberg.org/forgejo/forgejo/actions/runs/9541/jobs/5#jobstep-7-839
> FATAL ERROR: log.Error has been called: 2024/03/28 14:30:33 ...it/repo_attribute.go:313:func2() [E] Unable to open checker for 3fa2f829675543ecfc16b2891aebe8bf0608a8f4. Error: failed to run attr-check. Error: exit status 128
Stderr: fatal: this operation must be run in a work tree
Co-authored-by: oliverpool <git@olivier.pfad.fr>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/2939
Reviewed-by: oliverpool <oliverpool@noreply.codeberg.org>
Co-authored-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
Co-committed-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
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