Support NetBSD.

[snimmagadda]

sys-info gained NetBSD support via FillZpp/sys-info-rs#91. Add NetBSD to the target_os so that this crate works on NetBSD…

$ uname -a
NetBSD  9.99.106 NetBSD 9.99.106 (GENERIC) #0: Thu Nov 17 17:40:09 IST 2022  skn@:/home/skn/obj/sys/arch/amd64/compile/GENERIC amd64

$ cargo run
   Compiling effective-limits v0.5.4 (/home/skn/effective-limits.rs)
    Finished dev [unoptimized + debuginfo] target(s) in 1.05s
     Running `target/debug/test-limited`
Error: SysInfo

$ git stash pop
On branch master
Your branch is up to date with 'origin/master'.

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
        modified:   Cargo.toml
        modified:   src/lib.rs

no changes added to commit (use "git add" and/or "git commit -a")
Dropped refs/stash@{0} (89bb3044e12cd68460ab30081d26f2cd9b4e87ca)

$ cargo run
   Compiling effective-limits v0.5.4 (/home/skn/effective-limits.rs)
    Finished dev [unoptimized + debuginfo] target(s) in 1.05s
     Running `target/debug/test-limited`
4037632

[rbtcollins]

I think this is good and we're actually seeing CI noise.