Use rustup's minimal profile during CI on FreeBSD
Use rustup's minimal profile during CI on FreeBSD

This should fix CI on FreeBSD after Rustup 1.20.0 was released, and save
time as well.

nix-rust/nix,nix-rust/nix,carllerche/nix-rust,asomers/nix,geofft/nix-rust,geofft/nix-rust,asomers/nix,carllerche/nix-rust,carllerche/nix-rust,geofft/nix-rust