Auto merge of #2187 - JohnTitor:fix-freebsd-ci, r=JohnTitor
Auto merge of #2187 - JohnTitor:fix-freebsd-ci, r=JohnTitor

Set `RUSTUP_IO_THREADS=1` to avoid the installation failure on FreeBSD CI

r? `@ghost`

rust-lang/libc,rust-lang/libc,rust-lang/libc