Allow spaces in shebang lines

[jwnrt]

Any character is allowed in a shebang line including spaces. This is usually used with /usr/bin/env -S to split the line into arguments.

Most people using shebangs for cargo-script today will probably need to use #!/usr/bin/env cargo +nightly -Zscript so I've added this as a test.

[amaanq]

thanks! I just regenerated with the latest cli version and amended on top of your last commit