Spurious cargo test failure in alt_registry::no_api

[RalfJung]

Seen on aarch64-apple

---- alt_registry::no_api stdout ----
running `/Users/runner/work/rust/rust/build/aarch64-apple-darwin/stage2-tools/aarch64-apple-darwin/release/cargo check`
running `/Users/runner/work/rust/rust/build/aarch64-apple-darwin/stage2-tools/aarch64-apple-darwin/release/cargo login --registry alternative`

thread 'alt_registry::no_api' (2024432) panicked at src/tools/cargo/tests/testsuite/alt_registry.rs:821:10:

test failed running `/Users/runner/work/rust/rust/build/aarch64-apple-darwin/stage2-tools/aarch64-apple-darwin/release/cargo login --registry alternative`
error: could not exec process `/Users/runner/work/rust/rust/build/aarch64-apple-darwin/stage2-tools/aarch64-apple-darwin/release/cargo login --registry alternative`: could not execute process `/Users/runner/work/rust/rust/build/aarch64-apple-darwin/stage2-tools/aarch64-apple-darwin/release/cargo login --registry alternative` (never executed)

Caused by:
    Broken pipe (os error 32)

Stack backtrace:
   0: <std::backtrace::Backtrace>::create
   1: <std::io::error::Error as anyhow::context::ext::StdError>::ext_context::<cargo_util::process_error::ProcessError>
   2: <cargo_util::process_builder::ProcessBuilder>::output
   3: <cargo_util::process_builder::ProcessBuilder>::exec_with_output
   4: <cargo_test_support::Execs>::run
   5: testsuite::alt_registry::no_api
   6: <testsuite::alt_registry::no_api::{closure#0} as core::ops::function::FnOnce<()>>::call_once
   7: test::__rust_begin_short_backtrace::<core::result::Result<(), alloc::string::String>, fn() -> core::result::Result<(), alloc::string::String>>
   8: test::run_test::{closure#0}
   9: std::sys::backtrace::__rust_begin_short_backtrace::<test::run_test::{closure#1}, ()>
  10: <std::thread::lifecycle::spawn_unchecked<test::run_test::{closure#1}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  11: <std::sys::thread::unix::Thread>::new::thread_start
  12: __pthread_cond_wait
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: cargo_test_support::panic_error::pe
   3: <cargo_test_support::Execs>::run
   4: testsuite::alt_registry::no_api
   5: <testsuite::alt_registry::no_api::{closure#0} as core::ops::function::FnOnce<()>>::call_once
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
---- alt_registry::no_api stdout end ----

failures:
    alt_registry::no_api

Cc @weihanglo @epage