change signature of `chown` to not accept `Option`s

[japaric]

get_pty now uses either "tty"'s gid or the effective group ID

[github-actions[bot]]

Number of dependencies and binary size impact report

Metric	main	PR #768	Delta
Direct dependencies	3	3	-
Total dependencies	4	4	-
Binary size	1021.6 KiB	1021.7 KiB	-
Text size	593.4 KiB	593.5 KiB	-

Dependencies diff

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

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.02% :warning:

Comparison is base (fbfbabd) 55.24% compared to head (d358128) 55.22%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #768 +/- ## ========================================== - Coverage 55.24% 55.22% -0.02% ========================================== Files 72 72 Lines 9840 9845 +5 ========================================== + Hits 5436 5437 +1 - Misses 4404 4408 +4 ``` | [Files Changed](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/768?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=memorysafety) | Coverage Δ | | |---|---|---| | [src/exec/use\_pty/parent.rs](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/768?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=memorysafety#diff-c3JjL2V4ZWMvdXNlX3B0eS9wYXJlbnQucnM=) | `0.00% <0.00%> (ø)` | | | [src/system/mod.rs](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/768?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=memorysafety#diff-c3JjL3N5c3RlbS9tb2QucnM=) | `81.92% <0.00%> (-0.44%)` | :arrow_down: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/768/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=memorysafety)

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