rustPlatform.fetchCargoVendor: set a custom User-Agent to avoid crates.io 403

Author: andresilva

pkgs/build-support/rust/fetch-cargo-vendor-util.py

@@ -40,6 +40,8 @@ def create_http_session() -> requests.Session:
         status_forcelist=[500, 502, 503, 504]
     )
     session = requests.Session()
+    # crates.io blocks the default python-requests/<version> User-Agent
+    session.headers["User-Agent"] = "nixpkgs fetchCargoVendor (https://github.com/NixOS/nixpkgs)"
     session.mount('http://', HTTPAdapter(max_retries=retries))
     session.mount('https://', HTTPAdapter(max_retries=retries))
     return session