update self_check function to work with sudo invoked through setuid wrapper

[japaric]

thanks @r-vdp for the initial implementation.
co-authored by @rnijveld

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01% ⚠️

Comparison is base (e2edeca) 55.24% compared to head (691022b) 55.23%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #772      +/-   ##
==========================================
- Coverage   55.24%   55.23%   -0.01%     
==========================================
  Files          72       72              
  Lines        9842     9841       -1     
==========================================
- Hits         5437     5436       -1     
  Misses       4405     4405              

Files Changed	Coverage Δ
src/common/error.rs	9.80% <0.00%> (ø)
src/sudo/mod.rs	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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[squell]

Hat tip to @yorickvP for noticing, as well.

[github-actions]

Number of dependencies and binary size impact report

Metric	main	PR #772	Delta
Direct dependencies	3	3	-
Total dependencies	4	4	-
Binary size	1021.7 KiB	1021.5 KiB	-
Text size	593.5 KiB	593.2 KiB	-

Dependencies diff

 └─ sudo-rs [v0.2.0]
    ├─ glob [v0.3.1]
    ├─ libc [v0.2.147]
    └─ log [v0.4.20]

[r-vdp]

Cool, I didn't get the time to make a PR for this patch yet, but glad to see it merged!