Remove the unstable warning and use /etc/sudoers(-rs) as the sudoers file

[rnijveld]

Fixes #525

[github-actions[bot]]

Number of dependencies and binary size impact report

Metric	main	PR #635	Delta
Direct dependencies	5	5	-
Total dependencies	10	10	-
Binary size	1.1 MiB	1.1 MiB	+0.4%
Text size	652.5 KiB	652.5 KiB	-

Dependencies diff

```diff └─ sudo-rs [v0.2.0-dev.20230703] ├─ glob [v0.3.1] ├─ libc [v0.2.147] ├─ log [v0.4.19] ├─ signal-hook [v0.3.15] | ├─ libc [v0.2.147] | ├─ signal-hook-registry [v1.4.1] | | └─ libc [v0.2.147] | └─ cc [v1.0.79] └─ signal-hook-registry [v1.4.1] ```

[codecov[bot]]

Codecov Report

Patch coverage: 75.00% and project coverage change: +0.08 :tada:

Comparison is base (7f8ad2b) 86.70% compared to head (d24e403) 86.79%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #635 +/- ## ========================================== + Coverage 86.70% 86.79% +0.08% ========================================== Files 61 61 Lines 8605 8594 -11 ========================================== - Hits 7461 7459 -2 + Misses 1144 1135 -9 ``` | [Impacted Files](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/635?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=memorysafety) | Coverage Δ | | |---|---|---| | [src/sudo/mod.rs](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/635?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=memorysafety#diff-c3JjL3N1ZG8vbW9kLnJz) | `86.25% <75.00%> (+7.12%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/635/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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