`RUST_SCRIPT_BASE_PATH` reports the wrong path when rust-script executes with `--base-path` arg

[wmmc88]

RUST_SCRIPT_BASE_PATH does not report the correct base path when using rust-script's --base-path arg.

script.rs:

#![allow(unused_doc_comments)]

println!("{}", std::env::var("RUST_SCRIPT_BASE_PATH").expect("RUST_SCRIPT_BASE_PATH should always be set by rust-script"));

output:

❯ rust-script.exe .\script.rs
D:\git-repos\github\rust-script

❯ rust-script.exe --base-path 'D:\'  .\script.rs
D:\git-repos\github\rust-script

I expected the second run to print the updated base-path: D:\