Forward cargo package --list warnings (#2186)

Forward warnings from `cargo package --list` calls. Motivation is the `crates/jiter` crate in [jiter](https://github.com/pydantic/jiter):

```
$ cargo package --list
warning: readme `../../README.md` appears to be a path outside of the package, but there is already a file named `README.md` in the root of the package. The archived crate will contain the copy in the root of the package. Update the readme to point to the path relative to the root of the package to remove this warning.
```

src/source_distribution.rs

@@ -8,6 +8,7 @@ use ignore::overrides::Override;
 use normpath::PathExt as _;
 use path_slash::PathExt as _;
 use std::collections::HashMap;
+use std::io::Write;
 use std::path::{Path, PathBuf};
 use std::process::Command;
 use std::str;
@@ -153,8 +154,9 @@ fn add_crate_to_source_distribution(
     skip_cargo_toml: bool,
 ) -> Result<()> {
     let manifest_path = manifest_path.as_ref();
+    let args = ["package", "--list", "--allow-dirty", "--manifest-path"];
     let output = Command::new("cargo")
-        .args(["package", "--list", "--allow-dirty", "--manifest-path"])
+        .args(args)
         .arg(manifest_path)
         .output()
         .with_context(|| {
@@ -172,6 +174,10 @@ fn add_crate_to_source_distribution(
             String::from_utf8_lossy(&output.stderr),
         );
     }
+    if !output.stderr.is_empty() {
+        eprintln!("From `cargo {}`:", args.join(" "));
+        std::io::stderr().write_all(&output.stderr)?;
+    }
 
     let file_list: Vec<&Path> = str::from_utf8(&output.stdout)
         .context("Cargo printed invalid utf-8 ಠ_ಠ")?