fix: use std::env::args_os instead of std::env::args (#1698)

Apparently `std::env::args()` will panic during iteration if any
argument to the process is not valid Unicode:

https://doc.rust-lang.org/std/env/fn.args.html

Let's avoid the risk and just go with `std::env::args_os()`.

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[//]: # (BEGIN SAPLING FOOTER)
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with [ReviewStack](https://reviewstack.dev/openai/codex/pull/1698).
* #1705
* #1703
* #1702
* __->__ #1698
* #1697

codex-rs/arg0/src/lib.rs

@@ -30,7 +30,7 @@ where
     Fut: Future<Output = anyhow::Result<()>>,
 {
     // Determine if we were invoked via the special alias.
-    let argv0 = std::env::args().next().unwrap_or_default();
+    let argv0 = std::env::args_os().next().unwrap_or_default();
     let exe_name = Path::new(&argv0)
         .file_name()
         .and_then(|s| s.to_str())