Set a User-Agent for package archive downloads (#52177)

Send `User-Agent: codex-package` when downloading archives in
`scripts/codex_package/dotslash.py`.

GitOrigin-RevId: b12dc962b28d795704ba780b020fbf7ab91f5d50

scripts/codex_package/dotslash.py

@@ -11,7 +11,7 @@ import zipfile
 from dataclasses import dataclass
 from pathlib import Path
 from urllib.parse import urlparse
-from urllib.request import urlopen
+from urllib.request import Request, urlopen
 
 from .targets import TargetSpec
 
@@ -168,7 +168,8 @@ def download_archive(url: str, archive_path: Path) -> None:
     temp_path = archive_path.with_suffix(f"{archive_path.suffix}.tmp")
     temp_path.unlink(missing_ok=True)
     try:
-        with urlopen(url, timeout=DOWNLOAD_TIMEOUT_SECS) as response:
+        request = Request(url, headers={"User-Agent": "codex-package"})
+        with urlopen(request, timeout=DOWNLOAD_TIMEOUT_SECS) as response:
             with open(temp_path, "wb") as out:
                 shutil.copyfileobj(response, out)
         temp_path.replace(archive_path)